Electronic engine control

ABSTRACT

An electronic controller for an internal combustion engine provides a ratio control signal corresponding to a respective air/fuel ratio, and responds to an air flow signal, a fuel flow signal and the ratio control signal to control fuel flow as to make the ratio of air flow to fuel flow substantially equal to said respective air/fuel ratio. The ratio control signal is developed from a base run ratio control signal as modified in response to various parameters such as engine temperature, manifold pressure, idle, manifold vacuum, fuel temperature, wide open throttle, engine speed, and start. The controller also provides a speed-up circuit for promptly responding to change in air flow and dynamic braking for the fuel metering pump. The pump speed circuit includes a range extender. The controller further provides a timing advance control signal in response to air/fuel ratio and various engine parameters such as engine speed, manifold pressure, throttle position, engine temperature, air temperature, air/fuel ratio, and start.

This invention relates to engine controls and more particularly to thecontrol of fuel flow and ignition timing in connection with a sparkignited internal combustion engine. Still more specifically, thisinvention relates to the control of fuel flow and spark advance inresponse to a number of sensed engine conditions.

It is well known to control fuel flow in an internal combustion engine,especially to maintain an appropriate air/fuel ratio, as is disclosed inPriegel U.S. Pat. No. 3,817,225 issued June 18, 1974 for "ElectronicCarburetion System for Low Exhaust Emissions of Internal CombustionEngines." Priegel discloses a system wherein the rate of air flow andcertain other parameters are measured and used to control the drive of apositive displacement metering pump to supply fuel at an appropriateair/fuel ratio.

In such systems it is known to use an air flow transducer like thatdisclosed in Chapin United States Patent Application Ser. No. 783,612,filed Apr. 1, 1977 for "Air Flow Transducer," now U.S. Pat. No.4,089,215 issued May 16, 1978. The air flow as detected by suchtransducer is used in connection with an electronic control system forcontrolling the flow of fuel to maintain an appropriate air/fuel ratio.In connection with such control it is known to utilize a fuel supplysystem as disclosed in Chapin and Merrick United States PatentApplication Ser. No. 783,610, filed Apr. 1, 1977 for "Fuel System withMetering Pump for Internal Combustion Engines" now U.S. Pat. No.4,112,901 issued Sept. 12, 1978. It is also known to utilize such fuelsupply systems to supply fuel to a carburetor like that shown in ChapinUnited States Patent Application Ser. No. 783,611, filed Apr. 1, 1977for "Carburetor with Hollow Air Control Valve," now U.S. Pat. No.4,087,491 issued May 2, 1978. The present invention is directed to animproved electronic controller, particularly one that may be used withthe air flow transducer of Application Ser. No. 783,612 for controllinga fuel supply system like that disclosed in Application Ser. No.783,610.

The controller of the present invention is responsive not only to rateof air flow and rate of fuel flow, but also to barometric pressure,manifold pressure, air temperature, throttle position, fuel temperature,engine temperature, the use of accessories, start condition, and engineposition (and hence, indirectly, engine speed) for supplying fuel at anappropriate rate. It is well known to utilize microprocessors ofcomputers responsive to various engine conditions to provide fuelcontrol. One such system is shown in Moyer et al. U.S. Pat. No.3,969,614, issued July 13, 1976 for "Method and Apparatus for EngineControl."

The present invention also utilizes the electronic controller forcontrolling ignition timing. Conventionally, centrifugal means dependentupon engine speed and means responsive to manifold vacuum have been usedto advance the spark. Comparable spark advance has been achievedelectronically. One such electronic controller is disclosed in theaforesaid Moyer et al. U.S. Pat. No. 3,969,614. Another timing controlis shown in Crall et al. U.S. Pat. No. 3,978,833 issued Sept. 7, 1976for "Engine Control Circuit for Providing a Programmed ControlFunction."

Like the present invention, certain of the controllers of the prior arthave been used to provide what might be called the "best" performance.However, what is best depends upon a number of competing factors, suchas economy, ecology and drivability, the latter two being particularlysubjective. In any event, in accordance with the present invention fuelflow and ignition timing are controlled in a manner to provide differentrelationships to the engine conditions than have been found in thecontrols of the prior art.

Thus, the primary object of the present invention is to provide animproved electronic control of fuel flow and ignition timing as tooptimize fuel economy, exhaust emission, drivability, and moreparticularly the relationships among the three. More specific objectsand advantages of the present invention will become apparent fromconsideration of the following detailed description, particularly whentaken in connection with the appended drawings in which:

FIG. 1 is a diagrammatic illustration of a controlled air/fuel systemand ignition timing system for an internal combustion engine utilizingthe controller of the present invention;

FIG. 2 is a diagrammatic illustration of a preferred form of thecontroller 2 of the present invention showing the relationships amongthe respective control circuits;

FIG. 3 is a schematic diagram of the pressure signal circuits 3 of thecontroller 2;

FIG. 4 is a schematic diagram of a mass flow converter 4 for combiningthe air flow signal, the barometric pressure signal and the airtemperature signal to provide a measure of mass flow in the controller2;

FIG. 5 is a schematic diagram of a speed-up circuit 5 for correcting themass flow signal from the mass flow converter 4 for inertia lag;

FIG. 6 is a schematic diagram of an accelerator pump circuit 6 forproviding additional fuel flow upon acceleration in the controller 2;

FIG. 7 is a schematic diagram of pump driver circuitry 7 of thecontroller 2 for driving a metering pump providing fuel for the enginein response to a signal dependent upon air flow;

FIGS. 8 and 9 are schematic diagrams of respective parts I and II ofratio control circuitry 8 and 9 for providing a ratio control signal fordetermining the air/fuel ratio to be maintained by the pump drivercircuitry 7;

FIG. 10 is a schematic diagram of throttle bypass control circuitry 10in the controller 2;

FIG. 11 is a schematic diagram of the ignition timing control circuitry11 in the controller 2;

FIGS. 12 and 13 are schematic diagrams of respective parts I and II oftiming advance circuitry 12 and 13 for providing a timing advancecontrol signal to the timing control circuit 11; and

FIG. 14 is a graphical illustration of the respective timing advancecontrol characteristics provided by the timing advance circuitry 12 and13.

The present invention is useful in internal combustion engines havingair/fuel control systems wherein fuel is supplied in metered amountsproviding a particular desired ratio of air to fuel for engineoperation. In such systems, air flow to the intake manifold of theengine is controlled and measured, and air flow rate, usually inconjunction with other parameters, is used to develop a control signalused for providing fuel at the desired air/fuel ratio. In FIG. 1 thereis illustrated very generally a control system for supplying anappropriate mixture of air and fuel to the intake manifold 20 of aninternal combustion engine 22 and for supplying ignition sparks atappropriate times to the respective combustion chambers of the engine22. The engine 22 may be a multi-cylinder spark ignited reciprocatingengine, specifically one burning gasoline. The engine 22 may have aconventional ignition system 24 which includes the usual spark coil,spark plugs, distributor and associated components.

The system of FIG. 1 includes a carburetor 30 which, as shown, ispreferably conical. As a principal function of the carburetor 30 is tocontrol the rate of flow of air to an intake manifold of an engine, theconical carburetor 30 is sometimes referred to as a conical throttle.The opening of the conical throttle 30 is controlled by a throttle rod32 which may be connected, for example, to a conventional automobileaccelerator pedal. The throttle rod 32 may be connected through a crank34, a shaft 35 and gears 36 to control the throttle opening and hencethe rate of flow of air into the intake manifold 20. As this is theprincipal air flow and as the throttle 30 is the throttle by which theoperator controls engine speed, the throttle 30 may also be referred toas the main throttle. The throttle 30 is enclosed in a housing 38 whichfits over the intake manifold 20 of the internal combustion engine 22.The throttle control linkage passes through the housing 38 at the shaft35. The conical throttle 30 and its manner of operation may be asdescribed in the aforesaid patent application Ser. No. 783,611.

All air flowing into the intake manifold flows through the housing 38,flowing into the housing through a filter 42 and an air flow transducer44. The air flow transducer 44 measures the rate of air flow into, andhence out of, the housing 38 by producing a systematically relatedelectrical signal AIR FLOW on a conductor 46 which goes to thecontroller 2. More particularly, the air flow transducer 44 and itsmanner of operation may be as described in the aforesaid patentapplication Ser. No. 783,612. Such transducer comprises a rotor drivenby the entering air to produce a signal AIR FLOW formed as pulsesoccurring at a rate indicative of volumetric rate of air flow. Thecontroller 2 receives other signals from other sensors, as describedbelow and utilizes the various signals to provide appropriate fuel pumppower PUMP on a conductor 50 to a metering pump 52.

The metering pump 52 is supplied with fuel through a conduit 53 by asupply pump 54 from a fuel tank 56, with any excess fuel being returnedto the fuel tank 56 through a return conduit 58. A pressure regulatorvalve 59 maintains a predetermined reference pressure at the intake ofthe metering pump 52. The metering pump 52 supplies fuel to thecarburetor 30 through a conduit 60 and an equalizer valve 62. A feedbacksignal PUMP TACH indicative of pump speed is developed by a pumptachometer 64 coupled to the metering pump 52 to move therewith. ThePUMP TACH signal is a series of periodic pulses occurring at a rateproportional to pump speed. The metering pump 42 is a positivedisplacement pump so that the PUMP TACH signal is indicative of rate offuel flow. The PUMP TACH signal is fed back over a conductor 65 to thecontroller 2 which utilizes the feedback signal to assure that themetering pump 52 operate at the desired speed. Reference pressure isapplied to the equalizer valve 62 through a conduit 66. Such fuel supplysystem and its manner of operation may be as described in the aforesaidpatent application Ser. No. 783,610.

Also illustrated generally in FIG. 1 is a bypass throttle 68 whichoperates as an auxiliary air control for admitting a controlledadditional amount of air into the intake manifold 20, as may be calledfor by a signal B.P. SOL developed in the controller 2 and applied tothe bypass throttle 68 over a conductor 70, as described in greaterdetail in Chapin and Merrick U.S. Pat. Application Ser. No. 783,614,filed Apr. 1, 1977 for "Modulated Throttle Bypass," now U.S. Pat. No.4,108,127, issued Aug. 22, 1978.

Reference will now be made to the other sensors illustrated in FIG. 1. Abarometric pressure transducer 72 is disposed within the housing 38 andmeasures the ambient air pressure by producing an output signal BAROPRESS indicative of barometric pressure transmitted to the controller 2over a conductor 74.

An air temperature sensor 76 is also disposed within the housing 38 tomeasure ambient air temperature. Such senor may provide an output signalRt in the form of a resistance magnitude dependent upon temperature. Theoutput signal is coupled to the controller 48 over a conductor 78.

Fuel temperature is sensed by a fuel temperature sensor 80 disposedwithin the metering pump 52. The fuel temperature sensor may comprise atemperature sensitive diode which produces a fuel temperature signal FTCon a conductor 82 connected to the controller 2.

A throttle position sensor 84 is coupled to the shaft 35 and produces athrottle position signal TPV on a conductor 86 extending to thecontroller 2. The throttle position sensor may comprise a transformerwith a movable core and a split secondary winding. The core is moved bythe shaft 35 to produce an imbalance in the secondary winding. Theimbalance is then detected by a conventional circuit which produces ananalog signal TPV indicative of throttle position.

A wide open throttle sesor 88 is also coupled to the shaft 35. The wideopen throttle sensor may be in the form of a limit switch which isclosed when the throttle is moved to its extreme wide open condition.The closing of the switch applies a signal WOT to a conductor 90connected to the controller 2. For the controller 2 described below, thesignal WOT indicative of wide open throttle is a ground condition, theconductor 90 being otherwise at a positive potential.

An engine temperature sensor 92 may comprise a temperature sensitivediode disposed in the engine coolant. This transducer produces an enginetemperature signal ETS on a conductor 93 connected to the controller 2.

Manifold pressure is sensed by a manifold pressure sensor 94 coupled tothe manifold 20. The manifold pressure sensor 94 may operate in thefashion of the barometric pressure sensor 72 to provide a manifoldpressure signal MANIF PRESS on a conductor 95 connected to thecontroller 2.

An accessories sensor 96 may be used to indicate whether or not certainaccessories are being used as may load the engine, most notably an airconditioner. The detector may comprise a connection to the switchturning the air conditioner on and thus apply an appropriate signal ACCto a conductor 98 connected to the controller 2.

Similarly, a start condition may be sensed by a start sensor 100 whichmay comprise a connection to the switch starting the starting motor andthus develop a signal 12V ST on a conductor 102 connected to thecontroller 2.

In order to determine the speed and position of the engine, a run pickup104 is coupled to the distributor of the ignition system 24. The runpickup 104 may comprise an electromagnetic pickup sensing theinterruption of a magnetic field at a particular time in the distributorcycle, such as for example, 60° before top dead center for eachcylinder. An output signal RUN PICKUP in the form of periodic pulses isapplied over a conductor 106 to the controller 2 where it may be used todevelop a signal indicative of engine speed. The signal may also be usedin timing. Similarly, a start pickup 108 may be used to develop a signalSTART PICKUP useful in providing timing during a starting condition.Such signal may, for example, produce a pulse at 10° before top deadcenter over a conductor 110 connected to the controller 2.

To complete the description of the system illustrated in FIG. 1, thecontroller 2 produces a timing signal IGNITION PULSE in response to thesensed conditions and applies this signal over a conductor 112 to theignition system 24.

It should be noted that each of the conductors referred to that areshown as single lines in FIG. 1 may in fact comprise a pair or more ofconductors to provide the necessary paths for completion of therespective signal circuits. The completion of the conductors to thecontroller 2 are not all shown in order to avoid the confusion ofmultiple lines. In point of fact, each of the arrowheads extending fromthe respective sensors indicates the connection of the respectiveconductor to the controller 2. Similarly, in the remaining figures therespective conductors are shown at the input to the controller 2. Wherethe same signal is applied to different parts of the controller, thesame number will be used to identify collectively the conductors overwhich the signal is applied.

FIG. 2 is a diagrammatic illustration of the entire controller 2 showingthe connections from the respective sensors and showing theinterconnections between the various component circuits illustrated inFIGS. 3 through 14.

In FIG. 3 are illustrated the pressure circuits 3. These circuitsinclude a barometric pressure circuit 114 which receives the barometricpressure signal BARO PRESS from the barometric pressure transducer 72over the conductor 74 and produces on a conductor 116 an analog signalBPV systematically related to barometric pressure. The barometricpressure circuit 114 is essentially an amplifier with an output circuitto provide a signal of appropriate magnitude at an appropriate impedancelevel. Similarly, a manifold pressure circuit 118 receives the manifoldpressure signal MANIF PRESS from the transducer 94 over a conductor 95and produces a systematically related manifold pressure signal MPV, ananalog signal corresponding to the manifold pressure. The signal MPV isapplied to a conductor 120. The pressure circuits 3 also include amanifold vacuum circuit 122 which is essentially a subtraction circuitproviding a manifold vacuum signal MVV on a conductor 124 that is thedifference between the barometric pressure signal BPV and the manifoldpressure signal MPV. The signal MVV is therefore indicative of themagnitude of the vacuum in the manifold, that is, the negative pressurebelow barometric that exists in the intake manifold 20.

The mass flow converter 4, as shown in FIG. 4, combines the barometricpressure signal BPV with the air temperature signal Rt to produce asignal ADV indicative of air density and utilizes this signal to modifythe air flow signal AIR FLOW, which is indicative of volumetric rate offlow of air, to produce a signal MFV indicative of mass rate of flow ofair.

As shown in FIG. 4, the mass flow converter 4 includes a multipliercircuit 126 to which the barometric pressure signal BPV is applied onthe conductor 116 and the air temperature signal Rt is applied over theconductor 78, or in this instance, more properly between conductors 78,one of which is grounded. The signal BPV is applied to the+terminal ofan amplifier N4-5, 6, 7 through a resistor R39. Resistors R39 and R34form a voltage divider placing the signal at the+terminal in theappropriate scale range. The output of the amplifier N4-5, 6, 7 at pin 7is applied through a transistor Q6 to an output conductor 128. Aresistor R36 and the resistance Rt representing air temperature form avoltage divider providing the input to the-terminal of the amplifierN4-5, 6, 7 through a resistor R35. The air temperature sensor 76 has anegative temperature coefficient of resistance, whereby the resistanceof the air temperature signal Rt increases as temperature goes down.This, thus, introduces a multiplying factor into the amplifier N4-5, 6,7, causing the output on the conductor 128 to go up as temperature goesdown. This, of course, is the relationship between air density andtemperature, and the output signal ADV on the conductor 128 is thusrepresentative of air density provided the various circuit elements areof the appropriate magnitude. More particularly, the resistance of theresistor R36 is selected relative to the resistance of Rt, theresistance of the air temperature sensor 76, to make the responseapproximately linear over the desired range. For example, the resistanceof the resistor R26 may be made equal to the resistance of the signal Rtat 25° C.

As shown in FIG. 4, the mass flow converter 4 includes a signalconditioning circuit 130 which receives the air flow signal AIR FLOW onthe conductor 46. The air flow signal AIR FLOW is typically in the formof periodic pulses having positive and negative components occasioned bythe building up and collapsing of the magnetic field in the air flowdetector. The signal conditioning circuit 130 operates to convert theinput signals into a series of corresponding pulses of uniform magnitudeand duration. More particularly, transistors Q1 and Q2 cause a signal tobe developed across a resistor R4 that corresponds to the air flowsignal AIR FLOW. The AC component of this signal is applied through acapacitor C5 and a resistor R5 to a Schmitt trigger circuit thatproduces corresponding square wave pulses at N1-7. These square wavepulses are applied to pin 3 of a one-shot multivibrator N2. At the sametime the pulses are inverted by an inverter N1-1, 2, 3 and applied tothe same pin 3. This amounts to doubling the number of triggering pulsesapplied to the multivibrator N2. The multivibrator N2 thus producesoutput pulses of uniform duration and magnitude at pin 12 which pulsesare at twice the frequency of the input pulses at the conductor 46.These pulses are thus at a frequency corresponding to volumetric rate ofair flow.

The miltivibrator output pulses are applied over a conductor 136 to amultiplying circuit 138. These pulses act to turn on a transistor Q3 andturn off a transistor Q4 for the duration of each pulse. Thus, duringeach pulse the air density signal ADV is applied through the transistorQ3 to charge a capacitor C2 though a resistor R23. When the pulse isoff, the transistor Q3 is non-conductive, and the transistor Q4conducts, permitting the capacitor C12 to discharge through the resistorR23. The resistor R23 and capacitor C12 thus act as an integratingcircuit, the average voltage developed on the capacitor C12 beingproportional to the magnitude of the air density signal ADV times theproportion of time that the capacitor is charged by virtue of the pulsesfrom the multivibrator N2. That is, the integrated value is the productof pulse width, pulse height and pulse rate, pulse width being theduration of the multivibrator pulse (a constant), pulse height beingproportional to the air density, and pulse rate being proportional tothe rate of occurrence of the multivibrator pulses which is in turnproportional to volumetric rate of air flow. Thus, the signal developedon the capacitor C12 is proportional to the product of air density andthe volumetric rate of air flow. As density times volume is mass, theintegrated signal is thus proportional to mass rate of flow. Theintegrated signal is applied to an amplifier 142 wherein a potentiometerA1 adjusts the factor of proportionality. The amplifier output isapplied through a filter 144 to develop on a conductor 146 acorresponding signal MFV corresponding to the mass rate of flow of air.

The signal MFV indicative of mass rate of flow is applied to thespeed-up circuit 5 which acts to overcome the sluggishness of the airflow transducer 44. In this case, the speed-up circuit 5 essentiallytakes the derivative of the applied signal MFV, and after a gainadjustment effected by a potentiometer A4, the derivative is added tothe signal MFV at a terminal N3-10. The combined signal is thenamplified and appears at the terminal N3-8 as a signal AFV whichrepresents a compensated mass rate of air flow signal more accuratelyrepresentative of the true mass rate of flow. That is, the mass rate ofair flow as measured is necessarily a delayed measurement because theinertia of the measuring instrument precludes its instantaneous resposeto the changes in rate of air flow through the transducer and couplingof the transducer to the air flow is imperfect. The speed-up circuit 5notes a change in rate of flow by noting the magnitude of the derivativeor rate of change of the mass flow signal MFV. When there is arelatively fast rate of change, this indicates that there will besubstantially further future change, until the transducer reaches itsstable condition truly indicative of rate of air flow. Thus, by adding asignal related to the rate of change either positively or negatively,the combined air flow signal AFV is more representative of the stablecondition and hence more representative of the true rate of air flow.

In the circuit illustrated, the mass flow signal MFV is applied across avoltage divider formed by resistors R42 and R43. The portion of thesignal appearing across the resistor R43 is applied to an amplifierN3-5, 6, 7 to control a transistor Q13 to provide current flow throughthe transistor Q13 as to maintain the voltage drop across a resistor R44equal to that across the resistor R43. This current flows through adiode string D10-D11-D12-D13. This causes a potential drop across thediode string that varies with current flow, but non-linearly as diodeimpedance varies inversely with current. For this reason changes in themass flow signal MFV make smaller changes in the voltage drop across thediode string when the mass flow signal is higher. The change in signalacross the diode string is applied through a capacitor C21 and amplifiedby an amplifier N3-12, 13, 14 to produce a signal at the terminal N3-14proportional to the change in potential across the diode string. Apotentiometer A4 and a resistor R53 are connected in series from theterminal N3-14 and the 6-volt power supply. The 6 volt supply permitspositive and negative swings to the differential signal. The setting ofthe potentiometer A4 determines the gain of the amplifier N3-12, 13, 14.The differential signal at the terminal N3-14 is applied through aresistor R52 to add to the mass flow signal MFV. The summed signals areapplied through an amplifier N3-8, 9, 10 to produce compensated air flowsignal AFV on a conductor 148. The 6-volt supply is connected to theinput terminal N3-9 through a resistor R55 and a potentiometer A5 tooffset the effect of the connection of the 6 volt power supply to theamplifier N3-12, 13, 14.

The effect of the non-linear current-voltage characteristic of thediodes D10-D11-D12-D13 is to reduce the effect of the speed-up circuit 5at high rates of air flow where the air flow transducer 44 is bettercoupled to the air stream than at low rates of flow. Thus, a stepfunction at high rates of flow, as indicated by a high mass flow signalMFV, makes a relatively small change in the compensation signal asdeveloped at the terminal N3-14. This makes the compensation greatestwhere it is most needed.

The 11 volt power supply is momentarily applied through a capacitor C19when the controller 2 is first turned on. This momentarily causes atransistor Q4 to conduct to disable the speed-up circuit 5 at the start.

It is well known that a gasoline engine functions better uponaccelerating if the air-fuel mixture is enriched. It is thereforeconventional to provide an accelerator pump operating upon depression ofthe accelerator pedal to squirt a small additional amount of gasolineinto the carburetor upon change of accelerator pedal position in thedirection of further opening of the throttle. This function is achievedin the present invention by operation of the accelerator pump circuit 6illustrated in FIG. 6. The throttle position signal TPV is applied overthe conductor 86 to the accelerator pump circuit 6. The pump circuit 6comprises a long time constant pump circuit 150 and a short timeconstant pump circuit 152. In the long time constant pump circuit 150,any change in throttle position signal TPV changes capacitors C12 andC13 which are then discharged through a potentiometer A1 connected as avariable resistor and a resistor R18, with a time constant determined bythe position of the potentiometer A1. A portion of this signal is pickedoff a potentiometer A2 which determines the amplitude of the signal.This signal is amplified by an amplifier N2-5, 6, 7 to produce at aresistor R26 a signal of amplitude dependent upon the change in throttleposition signal TPV with a time constant dependent upon the setting ofthe potentiometer A1. An amplifier N2-1, 2, 3 is connected to assurethat the signal not go negative. A transistor Q2 and the connectionsthereto, particularly the voltage momentarily applied through acapacitor C14 when the system is first turned on, disables the circuitmomentarily to give time for the capacitors C12 and C13 to becomecharged initially by the throttle position signal TPV.

An RPM limit circuit 154 acts to limit the amplitude of the outputsignal from the long time constant pump circuit 150 to an upper limitdependent upon the engine speed. As will be described in greater detailin connection with FIG. 11, a signal RPMV indicative of engine speed isdeveloped on a conductor 156 in response to the run pickup signal RUNPICKUP applied over the conductor 106 from the run pickup sensor 104.The RPM limit circuit 154 assures that the signal at N2-13 not riseabove the engine speed signal RPMV. This provides an upper limit to theamplitude of the signal developed on the capacitors C12 and C13 andlimits the amplitude to a smaller voltage at lower speeds.

The short time constant accelerator pump circuit 152 is similar to thepump circuit 150 except that it operates with a shorter time constant asdetermined by the setting of a potentiometer A7 and provides a signal ofdifferent amplitude as determined by the setting of a potentiometer A6.The output of the short time constant accelerator pump circuit 152 isapplied through a resistor R27 to a summing amplifier N4-5, 6, 7 towhich the output of the long time constant accelerator pump circuit 150is also applied. The outputs of the long time constant accelerator pumpcircuit 150 and the short time constant accelerator pump circuit 152 aresummed in the summing amplifier N4-5, 6, 7, and the summed output isadded to the compensated mass air flow signal AFV applied over theconductor 148 through a summing resistor R37. These signals are summedin a summing amplifier N4-1, 2, 3, and the summed output is appliedthrough a resistor R41 to an output conductor 157 as the fuel controlsignal FCV.

A transistor Q1 responds to negative signals applied to the capacitorsC12 and C13 by grounding the fuel control signal FCV in the event ofnegative accelerator motion, that is, when the accelerator pedal islifted. This reduces the fuel flow more than would normally be the caseupon raising the accelerator pedal and acts to dispose of excess fuelalready in the fuel system. This eliminates a so-called CO spike in theexhaust emissions. Such spike is occasioned by the fact that the fuelfeed system contains some fuel accumulated in the system following themetering fuel pump. This fuel is in excess of the desirable amount forproper burning of the fuel when the throttle is being closed, reducingthe amount of air. To offset this somewhat and to reduce the excess fuelpromptly, the fuel control signal FCV is momentarily depressed.

An amplifier N4-12, 13, 14 and a diode D5 keep the output of the shorttime constant pump circuit 152 from going negative.

It has been discovered that cold engines will run more smoothly uponsudden accelerations if more fuel is added by the accelerator pumpaction than would be desirable when the engine is hot. A signal CLDindicative of a cold engine is applied to the accelerator pump circuits6 over a conductor 158. As will be described in greater detail below,the cold signal CLD is derived from the engine temperature signal ETSapplied to the controller 2 on the conductor 93. In the accelerator pumpcircuit 6, the cold signal CLD is applied to a transistor Q3 to changethe gain of the long time constant accelerator pump circuit 150 toincrease the gain when the engine is cold.

The fuel control signal FCV is in a sense the primary control voltagefor the pump driver circuit 7. As shown in FIG. 7, the pump drivercircuit 7 is essentially a circuit wherein the fuel control signal FCVapplied on the conductor 157 is compared to the pump speed signal PUMPTACH applied on the conductor 65, and the metering pump 52 is driven atsuch speed by the power applied at the conductor 50 as to place the fuelcontrol signal and the pump speed signal in appropriate ratio asdetermined by a ratio control signal RCV applied on a conductor 160. Theratio control signal RCV is developed in the ratio control circuits 8and 9 as illustrated in FIGS. 8 and 9 and discussed further below.Because the pump 52 is a positive displacement pump, pump speed is ameasure of rate of flow of fuel. Thus, the pump driver circuit 7 causesthe metering pump 50 to operate at such speed as to maintain the ratioof air flow (as indicated by the fuel control signal FCV) to fuel flow(as indicated by the PUMP TACH signal on the conductor 65) at theappropriate magnitude as demanded by the ratio control signal RCV on theconductor 160. Actually, of course, under conditions of acceleration theaccelerator pump circuit 6 causes the fuel control signal FCV to besomewhat different from the actual air flow signal AFV. Even so, one maybroadly construe the pump driver circuit 7 as maintaining fuel flow atan appropriate air/fuel ratio.

The fuel control signal FCV is applied on the conductor 157 through afollower circuit 162 and thence through a pump range extender circuit164 to the + input terminal of a differential amplifier 165.

The pump speed signal PUMP TACH is applied over the conductor 65 to asignal conditioning circuit 166 which operates substantially like thesignal conditioning circuit 130 described above in connection with FIG.4. That is, the pump speed signal PUMP TACH is in much the same form asthe air flow signal AIR FLOW and the signal conditioning circuit 166operates to convert the input signals into a series of correspondingpulses of uniform magnitude and duration at the terminal 12 of aone-shot multivibrator N5. As before, the output pulse rate is twice theinput pulse rate, at least under some conditions.

The output of the signal conditioning circuit 166 is applied to amultiplier circuit 168 which operates much like the multiplier circuit138 described in connection with FIG. 4. In this case the other input isthe ratio control signal RCV applied over the conductor 160. The outputof the multiplier circuit 168 is by way of an integrating circuitcomprising a resistor R21 and a capacitor C5 which operates to produceon the capacitor C5 a signal proportional to the product of the ratiocontrol voltage and the pump speed. This combined signal is applied tothe - input terminal of the differential amplifier 165. The amplifier165 thereupon acts to compare the fuel control signal FCV with thefraction of the fuel flow signal as demanded by the ratio control signalRCV.

The pump range extender circuit 164 is to permit relatively accuratefuel metering over a relatively wide range of speeds. The control rangeis limited by the permissible length of output pulses from themultivibrator N5. If the pulses are very short, the signals are toosmall for accuracy. On the other hand, if the pulses are made relativelylong, then the pump speed may be so great that the pulses occur sorapidly that the pulses actually overlap, making further controlimpossible as the signal can be no greater than fully on. To alleviatethis difficulty, the pump range extender circuit 164 cuts the effectivepulse rate in half at high metering pump speeds.

As shown in FIG. 7, the pump range extender circuit 164 receives thefuel control signal FCV from the follower circuit 162 and the ratiocontrol signal RCV from the conductor 160. Effectively, a differentialamplifier N3-5, 6, 7 compares the fuel control signal FCV with a portionof the ratio control signal RCV and develops a range control signal on aconductor 170 indicating which is the larger. As the ratio controlsignal RCV is a measure of the desired ratio between air flow (asrepresented by the fuel control signal FCV) and fuel flow (as indicatedby the PUMP TACH signal), the ratio control signal is itselfdeterminative of an air flow at which the pump speed exceeds some limit.That is, for any pump speed limit where it is desired to activate thepump range extender circuit 164, the ratio control signal RCV relatesthis limit to air flow. The relative resistances of resistors R5 and R7set the corresponding air flow limit for switching in the range extendercircuit 164. Thus, whenever the fuel control signal FCV is larger thanthe control level, as would indicate a demand for a relatively high pumpspeed, the range control signal is low, and whenever the fuel controlsignal is smaller, as would indicate a demand for a relatively low pumpspeed, the range control signal is high. The range control signal on theconductor 170 is applied to the inverter N4-1, 2, 3 to turn the inverteroff when the range control signal is low. This halves the number ofoutput pulses from the multivibrator N5, permitting twice as many pulsesand hence twice the pump speed before the range of the multivibratorcontrol is reached. This permits use of a longer period for themultivibrator and hence more accurate control at the lower speeds. Theresult of thus extending the range of the multivibrator is to reduce theoutput signal to the - terminal of the amplifier 165 by a factor of 2.To compensate for this, a high signal on the conductor 170 is appliedthrough a transistor Q2 to turn on a transistor Q1 which acts to shunt aresistor R9 in a voltage divider comprising resistors R9 and R10 ofequal resistance. This means that the shunting of the resistor R9 cutsin half the gain of an amplifier N2-5, 6, 7. Thus, the + input to theamplifier 165 is cut in half at the same time that the input to the -terminal is halved. The differential amplifier 165 thus produces a pumpcontrol signal on a conductor 172 indicative of whether the pump speedis above or below the desired speed. The pump control signal is appliedthrough a switching circuit 173 to a power amplifier 174. This switchingcircuit 173 is normally in the condition wherein a transistor Q4 is onand a transistor Q3 is off. This couples the conductor 172 to the poweramplifier 174. When the pump control signal on the conductor 172 isgreater than a reference potential on a conductor 176, a transistor Q5is turned on, which in turn turns on a transistor Q8, which in turnturns on a driving transistor QPD which supplies the driving currentPUMP for the pump 52 over the conductor 50. The pump 52 is then drivento make it travel at such speed that the pump speed signal PUMP TACHproduces a feedback signal at the - terminal of the differentialamplifier 165 as equals the fuel control signal as applied to the +terminal. Because the pump 52 is positively driven, it is promptlyspeeded up when fuel demand increases to follow demand accurately.

Should the fuel demand decrease, it is important that the fuel flow beshut down promptly in order that the fuel flow may also accurately andquickly follow the fuel damand when it decreases. This is achieved bythe application of the pump control signal on the conductor 172 torender conductive a transistor Q6 whenever the control signal dropsbelow the reference potential on the conductor 176. Conduction by thetransistor Q6 turns on transistors Q9 and Q10 which thereby shunts thepump circuit causing the motor to act as a generator and thereby removeenergy from the motor. This acts as a dynamic brake, causing the motorto slow down more promptly than were it merely to coast.

The effect of fuel temperature has so far been ignored. As fuel expandswith temperature, the mass of fuel indicated by the pump speed signalvaries with the temperature of the fuel. That is, at cold temperatures,a greater mass of fuel will occupy the same space. Thus, a fuel densitycircuit 178 is utilized to correct the pump tachometer signal forchanges in fuel density. The density is sensed by the fuel temperaturesensor 80, which may be a diode having a negative temperaturecoefficient of resistance. This produces a fuel temperature signal FTCat the conductor 82 in the form of a resistance which rises astemperature goes down. A voltage divider comprising resistors R63 andR64 sets an operating level to match the resistance of the fueltemperature sensor at some nominal temperature, such as 25° C. Thissignal is applied through a follower circuit N6-5, 6, 7 to a conductor180. This establishes the operating reference level. The gain of thecircuit is determined by the setting of a potentiometer A1 connectedbetween the conductor 180 and a resistor R66 connected to the conductor82. The signal at the tap of the potentiometer A1 is the sum of thereference level and a portion of the signal developed across the fueltemperature sensor 80. It is thus a measure of fuel temperature. Suchsignal is applied to an amplifier N6-1, 2, 3, the output of which isapplied to pin 7 of the multivibrator N5. This modifies the timeconstant of the multivibrator to provide longer pulses when the fuel iscolder and hence more dense and shorter pulses when the fuel is warmer.This compensates for changes in the density of the fuel.

An optional feature is the connection of a transistor Q14 to N5-2 and 4and the circuit for turning the transistor Q14 on. The transistor Q14 isturned on by a signal ALCOHOL applied to a conductor 182. When thetransistor Q14 is turned on the time constant of the multivibrator ischanged. This permits an alternative setup to the signal conditioningcircuit 166 whereby pulses of different length may be produced when adifferent fuel is used, as for example, alcohol. Thus, when such fuel isused in lieu of the regular fuel, a signal may be applied to theconductor 182 to modify the time constant of the multivibrator N5accordingly.

The purpose of the switching circuit 173 is to shut off the meteringpump 52 when the engine is not running. More particularly, the circuit173 is designed to turn off the pump 52 when the engine speed signalRPMV, as applied to the conductor 156, indicates that the engine isturning at less than idle speed and hence is not running. This acts toprevent flooding of the engine if the ignition switch is left on whilethe engine is stopped. The level indicative of idle is determined by theresistance of a resistor R17 connected in a voltage divider including aresistor R16. The engine speed signal is applied from the conductor 156to the + terminal of a comparator N1-5, 6, 7. When this signal fallsbelow the reference on the resistor R17, the output signal at N1-7 turnsoff the transistor Q4, thus turning off the power amplifier 174. At thesame time, this signal turns on a transistor Q3 which therebyshortcircuits the output of the differential amplifier 165 to assuredischarge of the output capacitor C4 when the engine is not running.This prevents accumulation of a charge on the capacitor C4 and hence thepresence of a control signal demanding fuel at the time the transistorQ4 is first turned on. This prevents an undesirable transient uponstarting.

In respect to starting, it is of course important to override theturning off of the transistor Q4 when one wishes to start the engine.This is achieved by applying the start signal 12V ST to the conductor102 to override the engine speed signal RPMV at the input to thecomparator N1-5, 6, 7 and thus assure turning on of the transistor Q4and turning off of the transistor Q3 upon starting the engine.

The ratio control circuits 8 and 9 as shown in FIGS. 8 and 9,respectively, develop the signal RCV corresponding to a desired air tofuel ratio. There is circuitry for developing a basic run ratio signalfor the normal steady state condition with various other circuits formaking adjustments in such signal for various transient conditions suchas to provide enrichment during idle, when starting, and when cold andfor certain conditions where extra power is required for drivabilityirrespective of economy or ecology. Many of these adjustments aresomewhat empirical, based upon a particular engine and the vehicle it ispropelling. As indicated above, the circuitry is to provide suitableoptimization of economy, ecology and drivability and suitable trade-offsamong the three. In general, the circuit illustrated is suitableparticularly for a socalled lean-burn engine. That is one in which theair to fuel ratio is well above the stoichiometric ratio, withsubstantially more air than is needed for combustion.

The basic run ratio is determined by a run ratio circuit 184 which isessentially a potentiometer connected between a conductor 186 andground. The adjustment of a potentiometer KP determines the run ratiowhich may, for example, be set to be 20:1. The conductor 186 is at areference potential of 6 volts under steady state conditions when theengine is hot. It is varied pursuant to a temperature control signal ENRV applied to the conductor 186 from circuitry shown in FIG. 9 anddiscussed further below. The signal picked off the potentiometer KP isapplied through a resistor R18 to a conductor 188, whence it passesthrough a buffer amplifier 190 to become the ratio control signal RCV onthe conductor 160.

Referring now to FIG. 9, the signal ENR V applied to the run ratiocontrol circuit is developed by a cold enrichment circuit 192. The inputto this cold enrichment circuit 192 is the engine temperature ETSapplied to the conductor 93. This signal is basically a resistancesignal created by the negative temperature coefficient of resistance ofa diode comprising the temperature sensor 80 placed in the coolant ofthe engine. A voltage is developed on this sensor 80 by way of a 6-voltpower supply and a resistor R10, the resistances of the sensor 80 andthe resistor R10 forming a voltage divider. The resistor R10 determinesthe range of signal levels on the conductor 93 as the resistance of thesensor 80 changes with temperature.

Basically, the cold enrichment circuit 192 operates by comparison of theengine temperature signal ETS with a reference potential developed on aconductor 194. In the circuit illustrated in FIG. 9, this referencepotential is 0.6 volts as developed by a reference potential circuit196. When the signal ETS is below 0.6 volts, the engine may beconsidered to be warmed up. The resistor R10 determines the temperatureat which the signal reaches such level, which may, for example,correspond to 180° F. A potentiometer A2 provides a tap that may beadjusted to select a desired portion of the difference between theengine temperature signal ETS and the reference potential on theconductor 194. This sets the slope of the characteristic curve anddetermines the rate at which the signal ENR V on the conductor 186varies with engine temperature. The signal at the tap of thepotentiometer A2 is compared with the reference potential on theconductor 194 in a comparator comprising N1-1, 2, 3.

When the engine is warmed up, the signal picked off at the tap is lessthan 0.6 volts, and the output of the comparator keeps a transistor Q6turned off. This allows the 6-volt power supply signal to be appliedthrough a resistor R18 to a follower circuit N3-5, 6, 7 to the conductor186. On the other hand, when the signal at the tap rises above thereference level the transistor Q6 is caused to conduct through resistorsR18, R19 and R20, thereby reducing the input to the follower N3-5, 6, 7in proportion to the signal difference between the signal on the tap ofthe potentiometer A2 and the reference potential 0.6 volts.

In general, the slope of the characteristic curve is set to provide fordrivability when the engine is cold. This is a relatively short periodof time, yet it is critical in car operation as it is important that onebe able to start one's car without stalling and without unevendrivability that would be annoying, if not entirely unsafe. On the otherhand, as the engine warms up past the critical region, but before it isfully warmed up to its operating temperature, it becomes more importantto meet emissions requirements. To this end, an auxiliary referencepotential circuit 198 provides an auxiliary reference potential on aconductor 200. The auxiliary reference potential on the conductor 200 ismade slightly higher than the reference potential on the conductor 194,as, for example, about 0.65 volts. This is set by the position of apotentiometer A4 to correspond to some particular engine temperature,for example, 75° F. It is the nature of the reference potential circuits196 and 198 that the potential at their outputs cannot go above theselected reference potentials, while permitting the voltage to go belowsuch values. This means that when the engine is very cold, that is,below the temperature corresponding to the reference set by thepotentiometer A4, current flows through the transistor Q6 and flowspartly through a resistor R22 as well as through the resistor 20. Theenrichment signal ENR V therefore varies with engine temperatureaccording to a temperature characteristic having a slope that isrelatively steep, assuring substantial enrichment. Once, however, theengine temperature rises above the temperature corresponding to thesetting of the potentiometer A4, current ceases to flow through theresistor R22 to the conductor 200. Thereafter the enrichment voltagevaries as a somewhat different function of engine temperature with aflatter slope, until the temperature rises to the temperaturecorresponding to 0.6 volts on the conductor 194, which may be consideredoperating temperature. At that temperature, the transistor Q6 ceases toconduct and the enrichment signal ENR V is at the 6-volt referencelevel.

As mentioned above, one of the more difficult times in operation of aninternal combustion is at the start. It is helpful under startconditions to provide additional fuel flow to assure starting. In thecircuit of FIG. 9, this is achieved by a cold start enrichment circuit202. This circuit is activated by application of a starting signal 12VST on the conductor 102. This enables a transistor Q4 to apply theengine temperature signal ETS to the cold start enrichment circuit 202.This circuit 202 operates much as the cold enrichment circuit 192 todraw additional current through the resistors R18 and R19 to reduce theenrichment control signal ENR V on the conductor 186, thus reducing theultimate ratio control signal and causing a greater amount of fuel to besupplied by the metering pump 52. In this case, the enabling of thediode Q4 applies the engine temperature signal ETS to a capacitor C2which holds the voltage after the start signal is removed. Thecapacitance is then discharged through a potentiometer A3 over a periodof time as, for example, 10 seconds. The signal developed on thepotentiometer A3 is compared with the reference potential on theconductor 194 to control a transistor Q5 in the manner of the transistorQ6 of the cold enrichment circuit 192, adding enrichment. As the chargeon the capacitor C2 is dissipated through the potentiometer A3, theadded cold start enrichment gradually tapers off. Thus, the cold startenrichment continues for a time after the start switch is disengaged anddies out after a short period during which the engine almost surelystarts and reaches a relatively stable condition where it can remain inoperation after the cold start enrichment has been dissipated.

It may be noted that the cold enrichment circuit 192 provides anadditional output signal through a resistor R17 to a start circuit 204.This provides a signal corresponding to engine temperature to anamplifier comprising a differential amplifier N1-8, 9, 10 and itsassociated components. The gain of the amplifier is determined by thesetting of a potentiometer A1 connected as a variable resistor. Thepurpose of the start circuit 204 is to provide a suitable fuel controlsignal FCV irrespective of air flow through the air flow transducer 44.This enables fuel to be supplied in order to get the engine started inthe first place. There are two enabling signals applied to the startcircuit 204: one is the wide open throttle signal WOT applied on theconductor 90, and the other is the starting switch indicator 12V STapplied on the conductor 102. As stated above, the wide open throttlesignal WOT is at ground when the throttle is fully open; otherwise thesignal is normally held high by the 12-volt potential applied through aresistor R43 to the conductor 90. The normally high wide open throttlesignal WOT enables a transistor Q1 which then acts to turn off atransistor Q2. This permits a 12-volt start signal applied to theconductor 102 to enable a transistor Q3 to apply the output oftheamplifier N1-8, 9, 10 to the conductor 157 as the fuel control signalFCV. The magnitude of this signal is thus dependent upon the signal fromthe cold enrichment circuit 192 and provides a fuel control signal FCVdemanding an amount of fuel that depends upon the engine temperaturesignal ETS at the time the starting switch is engaged. The function ofthe WOT signal is to disable the transistor Q3 when the throttle is wideopen. When the WOT signal is low, indicating a condition of wide openthrottle, it disables the transistor Q1, thereby enabling the transistorQ2 to ground the 12-volt start signal. This shuts the metering pump offduring cranking when the throttle is wide open, thus providing anopportunity to clear the engine of flooding merely by flooring theaccelerator pedal and turning on the start switch to crank the engine.

Also responsive to the engine temperature signal ETS is a cold circuit206 wherein a comparator N1-5, 6, 7 senses when the engine temperaturesignal ETS rises above the reference potential on the conductor 194 andproduces an output signal CLD indicating that the engine is coldwhenever the engine temperature signal is above the reference. This CLDsignal is applied to the conductor 158 by which it is connected to theaccelerator pump circuit 6 as described above.

As noted above, the present engine control is designed to operate anengine with a lean air to fuel ratio, such as a ratio of 20:1, when theengine is in its cruise condition. Such a lean mixture is unsuitablewhen the engine is idling, as it will cause misfires. It is thereforedesirable to provide a richer ratio upon idle. This is the function ofan idle ratio limit circuit 210. An idle condition could be sensed bysensing the engine speed as indicated by the engine speed signal RPMV.However, in the circuit illustrated, the mass rate of flow of air signalMFV is utilized as an indication of the idle condition. When the engineis idling and the throttle is depressed to accelerate the engine, theengine speed does not immediately change because of the inertia of theengine and its load. The air flow sensor thus responds more promptly toa change from idle. Further, when the engine is under load there is agreater air flow for the same engine speed.

As shown in FIG. 8, the mass rate of flow of air signal MFV is appliedover the conductor 146 to the idle ratio limit circuit 210. The signalMFV is compared to a reference potential developed across resistor R3from the 6-volt power supply. This sets a break point for the controlcharacteristic. The reference potential is set slightly above the signalMFV at idle; thus when the signal MFV is below the reference signal, theidle ratio limit circuit 210 takes the engine to be at idle. When thesignal rises above the reference, an output signal is developed across aresistor R7 corresponding to the amount the signal MFV is above thereference. A potentiometer A2 is connected between the resistor R7 andthe conductor 186. The tap on the potentiometer A2 thus picks off asignal between that developed across the resistor R7 and the signal ENRV. The position of the potentiometer determines the magnitude of theeffect of the idle ratio limit circuit. As indicated above, it isdesirable that the engine operate at idle at the leanest ratio that itwill operate smoothly without misfire. The lean limit may be, forexample, an air/fuel ratio of 16:1. The signal picked off thepotentiometer A2 is applied to the + terminal of an amplifier N2-1, 2, 3which acts to prevent its output on the conductor 188 from rising abovethe idle limit control signal. This means that even though the run ratiomay be set at 20:1 under idle conditions, the idle ratio limit circuitwill limit the ratio control signal to correspond to a ratio of 16:1.Further, as the engine goes above idle toward its normal run conditionthe mass flow signal MFV causes the idle ratio limit circuit to increasethe limitation of the ratio control voltage along a slope until the runratio or some other limit as described below is reached.

It has been found that when starting a car, even with the engine warmedup, the normal run ratio is too lean for proper combustion when thecombustion chambers are not hot. That is, after a car has been standingonly a brief time, the combustion chambers will be much below theiroperating temperature, even though the engine coolant temperature is inits operating range. When the engine coolant is cold, as indicated bythe engine temperature signal ETS, the cold enrichment circuit 192provides additional enrichment to avoid the problem. However, when theengine is not cold a start enrichment circuit 212 is provided to addenrichment. In this circuit 212, the closing of the ignition switch tostart the engine applies the 12V ST signal to the conductor 102 which isapplied through a transistor Q5 to charge a capacitor C2. This chargewill remain even after the 12-volt start signal 12V ST is removed untilsuch time as the charge leaks off through a resistor R16 and apotentiometer A1 as well as through resistors R14 and R15. The timeconstant for such discharge is made whatever may be convenient for aparticular engine, such as 30 seconds. The charge on the capacitor thusdevelops a signal on the tap of the potentiometer A1 that decreases withtime after the 12V ST signal is removed. The signal at the tap isapplied through an amplifier N1-12, 13, 14 to enable a transistor Q6 andtransfer the signal to the + terminal of the amplifier N2-1, 2, 3. Thisreduces the input thereto in accordance with the start enrichment signalas picked off from the potentiometer A1. The gain of the circuit is, ofcourse, controlled by the setting of the potentiometer A1.

Another circumstance that presents drivability problems is operation atlow manifold vacuum. When operating at low manifold vacuum, as at arelatively low engine speed, opening the throttle has little effect onpower, for the pressure differential is so small that little additionalair flows and hence little additional fuel is supplied. It is thereforedesirable to increase power under such circumstances by providing anenriched air/fuel ratio. This is achieved by a power I circuit 214 (FIG.8). The manifold vacuum signal MVV is applied over the conductor 124 tothe power I circuit 214. The power I circuit is essentially the same asthe idle ratio limit circuit 210 and operates to place an upper limit onthe ratio control signal RCV. That is, if the air/fuel ratio is notlimited by some other control signal, it will be limited by the power Ioutput. Thus, when the manifold vacuum signal MVV as applied over theconductor 124 falls below the reference signal developed across aresistor R33, the power I circuit limits the potential on the conductor188 to prevent the ratio control signal from going above somepredetermined limit, such as that corresponding to an air/fuel ratio of18:1. This limit rises as the manifold vacuum signal rises above thecontrol limit. The effect of the power I circuit is to be concerned morewith power than with ecology or economy. That is, for drivability andfor power as needed, the power I circuit will override the normal runratio.

Another circumstance requiring power ahead of ecology or economy is inmatters of emergency when it is important to accelerate rapidly, as inpassing a truck or avoiding difficulty. It is important to be able toget substantial additional power. This is achieved by a power II circuit216 (FIG. 8). This circuit is activated by the wide open throttle signalWOT applied over the conductor 90. As stated before, when the throttlegoes wide open, the WOT signal goes to ground. This causes a transistorQ1 to turn off, thereby causing a transistor Q2 to conduct, and thusplacing one end of a resistor R11 at ground, the other end beingconnected through a potentiometer A3 to the conductor 186. Grounding theresistor R11 thus reduces the potential at the tap of the potentiometerA3, depending upon where the potentiometer A3 is set, and an amplifierN3-8, 9, 14 then operates like the power I circuit to provide anotherupper limit to the signal on the conductor 188. This signal would, forexample, be equivalent to a ratio of perhaps 14:1. As an alternative itwould be possible to apply a ramp signal, that is, a signal that varieswith throttle position such as a signal based upon the throttle positionsignal TPV, which ramp signal introduced the power II limit gradually,as in the case of the power I signal.

It is desirable to have even more power for acceleration when the car isalready going at relatively high speed. A power III circuit 218 (FIG. 9)provides such additional power by providing a still lower air/fuelratio. The power III circuit receives its control input from thetransistor Q1 in the power II circuit (FIG. 8). That is, the power IIIcircuit is enabled by the WOT signal at the same time that the power IIcircuit is activated. The activation signal PWR III is developed on aconductor 220. The conductor 220 is normally held at ground potential bythe transistor Q1. This disables a transistor Q7, which in turn disablesa transistor Q8, which in turn disables a transistor Q9. However, uponoccurrence of a WOT signal indicating a wide open throttle, thetransistor Q1 is made non-conductive, whereupon the conductor 220 israised to the higher potential of the 6-volt supply. This turns on thetransistor Q7, which in turn turns on the transistor Q8, which in turnturns on the transistor Q9. The engine speed signal RPMV is applied fromthe conductor 156 through a resistor R42 to the - input terminal of acomparator N4-1, 2, 3. The + terminal is held at a reference potentialpicked off a potentiometer A6. When the engine speed signal RPMV isbelow the reference potential set by the potentiometer A6, the output ofthe comparator N4-1, 2, 3 is high, and the transistor Q9 does notconduct. This leaves a conductor 222 at the 6-volt power supply level.On the other hand, when the engine speed signal RPMV exceeds thereference level set by the potentiometer A6, the output terminal N4-1goes low, whereupon the transistor Q9 conducts, causing a potential dropacross a resistor R35 which lowers the potential on the conductor 222.This signal X is then applied by the conductor 222 to an output circuitN3-10, 11, 13 (FIG. 8), which acts like the output circuits of the powerI and power II circuits to keep the ratio control signal RCV from risingabove some particular level. In this case the ratio limit is madeequivalent to the maximum power available, which occurs at about a 12:1air/fuel ratio.

Another problem arises in connection with deceleration of an engine. Indeceleration, the throttle is normally closed, resulting in highmanifold vacuum and low manifold pressure. The pressure may become solow as to be unable to support the combustion at the normal air/fuelratio. This results in unburned fuel in the exhaust. A decel ratio limitcircuit 224 (FIG. 8) operates to assure a richer mixture under certaindeceleration conditions. More particularly, the manifold pressure signalMPV on the conductor 120 is compared to a decel potential DPV applied ona conductor 226. The signal DPV is developed in a manner that will bediscussed further below in connection with FIG. 13. When the manifoldpressure is so low that the manifold pressure signal MPV is less thanthe reference signal DPV, transistors Q9 and Q10 are off. This causes adecel ratio limit signal to be applied to a conductor 228 as determinedby the setting of a potentiometer A6. This signal is applied to anoutput circuit N3-2, 4, 5 to limit the potential on the conductor 188 tolower the ratio control signal to the decel ratio limit if it is nototherwise more limited by some other control circuit. As the pressurerises so that the manifold pressure signal MPV is greater than the decelpressure reference signal DPV on the conductor 226, the signal on theconductor 228 is raised. This correspondingly raises the decel limitapplied by the output circuit N3-2, 4, 5 to the conductor 188. The limitis raised in accordance with how much the manifold pressure signal MPVexceeds the decel reference signal DPV. The slope of the characteristicis determined by the resistance of a potentiometer A5 connected as avariable resistor.

The throttle bypass control circuit 10 shown in FIG. 10 is substantiallythe same as the circuit shown in FIG. 5 of copending patent applicationSer. No. 783,614 and functions in the manner of the circuit described insaid copending patent application for controlling the flow of airthrough the bypass throttle 68. The circuit of the copending applicationincludes a temperature circuit 178 that is comparable to a cold idlecircuit 230 shown in FIG. 9. As described in the copending applicationin connection with such temperature circuit, the cold idle circuit 230operates in response to the engine temperature signal ETS on theconductor 93 to produce a cold idle signal C.I. on a conductor 232 whichis applied to the circuit of FIG. 10. The output of the throttle bypasscontrol 10 applies a control signal B.P. SOL. on the conductor 70 tocontrol the position of the bypass throttle 68 in the manner describedin the aforesaid application Ser. No. 783,614. An alternative throttlebypass control circuit would provide a more complicated characteristicfor control by the throttle position signal TPV to provide a progressivethrottle bypass control signal in which air flow increases more sharplywith throttle position when the throttle is wider open. This makes forsmoother control and drivability.

Adverting now to the timing control circuits, the ignition timingcontrol circuit 11 as shown in FIG. 11, basically responds to the runpickup signal RUN PICKUP on the conductor 106 and a timing controlsignal TCV as applied to a conductor 236 from the timing advancecircuits 12 and 13. The development of the timing control signal TCVwill be discussed further below in connection with FIGS. 12 and 13. Therun pickup signal RUN PICKUP and the timing control signal TCV areapplied to a trigger circuit 238 which produces an output pulse on aconductor 240 at a time determined by the timing control signal TCV.That is, the run pickup signal RUN PICKUP establishes a time reference,and at a time thereafter, as determined by the timing control signalTCV, an output trigger pulse TRIGGER is produced on the conductor 240.As mentioned above, the run pickup sensor 104 may be magnetic meansassociated with the ignition distributor in the ignition system 24 toprovide a time base identification of the position of the engine. Forexample, the run pickup signals RUN PICKUP may occur 60° before top deadcenter of each cylinder.

The run pickup signals RUN PICKUP are applied to a conditioning circuit242 which acts to convert the incoming signals to corresponding sharppulses suitable for triggering a bistable multivibrator 244 comprisingtransistors Q4 and Q5. When a pulse is applied from the conditioningcircuit 242, it turns on the transistor Q4 and thereupon turns off thetransistor Q5. It also turns off a transistor Q6 connected across acapacitor C10. The capacitor C10 is thereupon charged over a conductor246 at a rate determined by a position-line converter 248. The capacitorC10 charges until the voltage thereon as applied to the - input terminalof a comparator N4-5, 6, 7 rises to the potential on the + inputterminal. The latter voltage is determined by the timing control signalTCV applied over the conductor 236. The time it takes for the capacitorC10 to charge to the reference voltage determined by the timing controlsignal TCV is a time that is determined by the magnitude of the timingcontrol signal TCV. The time at which the capacitor C10 reaches thispotential will therefore occur at a particular time following aparticular run pickup pulse on the conductor 106 which triggered thebistable multivibrator 244. When the signal on the - input terminal ofthe comparator exceeds the reference potential on the + input terminal,the output goes negative applying a negative trigger signal TRIGGER toan ignition pulse circuit 250.

The ignition pulse circuit 250 acts in response to a trigger pulse toproduce a suitable ignition pulse on the conductor 112 for applicationto the ignition system 24. The ignition system thereupon acts to producea suitable spark discharge in a particular combustion chamber in theusual fashion.

The position-time converter 248 is controlled by the engine speed signalRPMV which is developed in an RPM circuit 252. In this case the runpickup signals RUN PICKUP are utilized to mark each cycle of rotation ofthe engine and hence develop a signal RPMV indicative of engine speed.The run pickup signals RUN PICKUP are conditioned by a signalconditioner 254 to produce corresponding pulses suitable for operating afrequency to voltage converter 256. The frequency to voltage converter256 operates to produce an output signal RPMV on the conductor 156 whichis proportional to the rate of incoming pulses. This signal is thereforeindicative of engine speed.

The position-time converter 248 operates to control the charging rate ofthe capacitor C10 and hence the time for the voltage thereon to reachthe reference level determined by the timing control signal TCV. Torelate engine position to time, it is necessary to know the speed ofrotation of the engine. This relationship is achieved by charging thecapacitor C10 at a rate dependent upon engine speed. In other words, ifthe engine is traveling twice as fast the capacitor C10 must be chargedtwice as fast in order that it reach a particular voltage level at thesame relative engine position, and hence at the same relative angle inrespect to the run pickup signal RUN PICKUP on the conductor 106. In theposition-time converter 248, the engine speed signal RPMV is applied tothe + terminal of an amplifier N3-1, 2, 3. With the current mirrorcircuit shown comprising resistors R33 and R34 and transistors Q1 andQ2, the current through the transistor Q2 and hence the current chargingthe capacitor C10 are proportional to the engine speed signal RPMV. Thismakes timing angles independent of engine speed. The ignition pulses onthe conductor 112 are thus instituted at a predetermined angularposition following each RUN PICKUP pulse on the conductor 106, asdetermined by the timing control signal TCV applied to the conductor236. The proportionality factor relating position to time is determinedby the resistance of a resistor R35.

During starting it is desirable to operate independently of the timingcontrol voltage, and instead to cause the ignition pulses to occurduring starting at a particular angular position in the cycle. A startcondition is sensed by a start timing circuit 258 which senses when theengine speed signal RPMV is less than a reference potential set on aresistor R40. Under such condition a signal is developed on a conductor260 to keep the transistor Q6 turned on until the engine speed risesabove the reference level. It may be presumed that the engine is in astart condition when the engine speed is below this reference level,which level is set below idle speed. This assures that the capacitor C10not be charged and the comparator N4-5, 6, 7 thus not produce an outputtrigger pulse during starting. Instead, the trigger pulse is derivedfrom the start pickup signal START PICKUP applied to the conductor 110.This signal is applied to a pulse conditioning circuit 262 whichoperates in much the fashion of the pulse conditioning circuit 242. Inthis case the output pulses operate to reset the bistable multivibrator244, at which time the multivibrator applies a trigger pulse directly tothe conductor 240. Ignition pulses are therefore produced at theterminal 112 at the appropriate time for starting as determined by thestart pickup pulses on the conductor 110.

The timing control signal TCV as applied to the conductor 236 isdeveloped in the timing advance circuits 12 and 13 of FIGS. 12 and 13 inresponse to signals from various of the sensors and signals developed inother parts of the controller. In general, the timing control signal TCVmay be said to be the sum of a number of timing advance signals withvarious limits superimposed. The signals are summed in a summing circuit264. The summing circuit 264 includes a summing point 266 and a summingresistor R8 connected between the summing point and ground. Signals fromthe various advance and limit circuits are applied through switches tothe summing point 266. These signals are summed across the resistor R8,and the summed signal is applied through a follower amplifier N3-1, 2, 3to develop the timing control signal TCV on the conductor 236.

As stated above, conventional timing controls include centrifugal meansfor advancing the spark as speed increases and vacuum means foradvancing the spark as manifold vacuum increases. The spark advance withengine speed is used to compensate for delays in flame propagation inthe burning of the fuel during each firing of a cylinder. Moreparticularly, because it takes time for the flame front to propagate, aspark that is timed properly at one speed will not be proper at otherspeeds. If speed is increased and the spark occurs at the same angularposition as before the increase, the engine moves faster relative to theflame front and the flame front is therefore relatively delayed. Tocompensate for this, the spark is advanced so that the burning startsearlier and peak pressure arrives at the appropriate time in the enginecycle.

In respect to the vacuum advance, it is evident that the flame frontwill advance more slowly at high vacuum. This is because the air densityis lower. Spark timing that is appropriate at one level of vacuum is toolate at greater vacuum because the flame front does not propagate asfast. Thus, as high vacuum levels it has been conventional to advancethe spark. In the circuit of the present invention spark is advancedpursuant to manifold pressure rather than manifold vacuum, because it isabsolute air density that is significant in the rate of propagation ofthe flame front. On the other hand, a circuit responsive to manifoldvacuum could be used and has the advantage that manifold vacuum sensorsare less expensive than manifold pressure sensors.

FIG. 14 illustrates typical controller timing characteristics producedby the timing advance circuits 12 and 13. More particularly, in FIG. 14Aare illustrated the RPM advance characteristic RPMA and the manifoldpressure advance characteristic MPA. The RPM advance characteristic is acurve of timing advance as a function of RPM and the manifold pressurecharacteristic is a curve of timing advance as a function of manifoldabsolute pressure (MAP) in inches of mercury.

The RPM advance characteristic RPMA is developed by an RPM advancecircuit 270 as shown in FIG. 12. As there shown, the RPM control signalRPMV is applied over the conductor 156 and through resistors R36 and R35to the + terminal of an amplifier N2-1, 2, 3. The - terminal is biasedby a reference potential developed at the junctions of resistors R34 andR32 connected as a voltage divider across the 6-volt power supply. Whenthe signal applied to the + terminal exceeds the bias level on the -terminal, a transistor Q10 is caused to conduct current in proportion tothe magnitude of the signal applied to the + terminal relative to thereference potential. A reference signal RPMI is developed by apotentiometer A7 and applied through a follower circuit to the tap of apotentiometer A5 connected as a variable resistor. The other side of thepotentiometer A5 is connected to the + terminal of an amplifier N1-1, 2,3. The transistor Q10 conducts through the potentiometer A5 and hencereduces the potential at the + terminal in proportion to the amount bywhich the RPM control signal RPMV exceeds the reference level applied tothe - terminal of the amplifier N2-1, 2, 3. When the RPM control signalRPMV is below the bias level of the amplifier N2-1, 2, 3 and thetransistor Q10 is therefore off, the reference signal RPMI is appliedthrough the potentiometer A5 to the terminal N1-3 of an amplifier N1-1,2, 3. As the RPM control signal RPMV rises above the bias level, thesignal at the terminal N1-3 falls proportionally. The signal applied atthe terminal N1-3 controls the flow of current through a transistor Q9to maintain the signal level at the emitter of the transistor Q9 at thelevel of the signal on the terminal N1-3. This determines the currentthrough a resistor R31 and thence the current through the transistor Q9.This current is applied through a switch S1-1 and a conductor 272 to asumming point 274 which is connected by a conductor 276 to the summingpoint 266. This signal on the conductor 272 corresponds to a number ofdegrees of spark advance and is the spark advance signal RPMA.

In the idle range, engine operation is somewhat unstable. It istherefore desirable that a fixed spark advance be applied during theidling of the engine. Idling may be taken as an engine speed below somereference speed and hence with an RPM control signal RPMV less than somereference potential, in this case the reference level established by thebias across the resistor R32. Up to that point, the transistor Q10 isdisabled and the reference potential RPMI is applied to the amplifierN1-1, 2, 3 to produce an output RPM advance control signal RPMAcorresponding to RPMI as illustrated in FIG. 14A.

Once the transistor Q10 becomes conductive, that is, when the RPMcontrol signal RPMV rises above the idle bias level, current flowsthrough the transistor Q10 and the potentiometer A5 to lower thepotential at the input terminal N1-3. This increases the flow of currentthrough the transistor Q9 and hence raises the output signal RPMA. Therelationship between the RPM control signal RPMV and the current flow inthe conductor 272 is determined by the resistance of the potentiometerA5, which thus determines the slope of the characteristic curve RPMA asshown in FIG. 14A.

At high speeds it is desirable that the rate of advance with speed beless. In fact, at high speeds, turbulence causes the fire front to sweepthe cylinder so rapidly that further advance is not necessary ordesirable. To limit the advance at high speed, a reference potentialRPMA STOP is established by a potentiometer A8. An amplifier N2-5, 6, 7and a diode D4 keep the terminal N2-6 from rising above the referencepotential RPMA STOP. This means that when the RPM control signal RPMVrises above the reference potential RPMA STOP, the potential at theterminal N2-3 is held to the level RPMA STOP. This puts an upper limitto the characteristic curve for the RPM advance signal as shown in FIG.14A.

The manifold pressure advance signal MPA is developed in a manifoldpressure advance circuit 278. This circuit responds to the manifoldpressure signal MPV applied to the conductor 120. The manifold pressuresignal MPV is amplified by a follower circuit comprising an amplifierN5-1, 2, 3 which develops a corresponding manifold pressure signal MPVBon a conductor 280. This signal is applied through a potentiometer A10and a resistor R28 to a pair of amplifiers N6-1, 2, 3 and N7-5, 6, 7.The signal is applied to the amplifier N6-1, 2, 3 by way of anintegrating circuit consisting of a capacitor C8 and a variable resistorA11. The integrating circuit effectively delays the application of thesignal to the amplifier N6-1, 2, 3. The outputs of the respectiveamplifiers are applied through respective diodes D4 and D5 to a terminal282 connected to ground through a resistor R31. The terminal 282 isbiased from the 6-volt power supply through a potentiometer A12 and aresistor R30, the potentiometer A12 and the resistances R30 and R31constituting a voltage divider. The amplifiers N6-1, 2, 3 and N7-5, 6, 7are connected so that the more positive output of the amplifierscontrols the diodes D4 and D5 decoupling the more negative output fromthe terminal 282.

Because the input to the amplifier N6-1, 2, 3 is applied by way of anintegrating circuit, the input thereto is delayed. Thus, when themanifold pressure signal MPV rises, the output of the amplifier N7-5, 6,7 rises at once, in unison with the manifold pressure voltage MPV,whereas the output of the amplifier N6-1, 2, 3 lags behind. Thus, theoutput of the amplifier N7-5, 6, 7 controls as atmospheric pressureincreases. On the other hand, the output of the amplifier N6-1, 2, 3also lags as the pressure drops. As this leaves the output of theamplifier N6-1, 2, 3 higher than the output of the amplifier N7-5, 6, 7,the amplifier N6-1, 2, 3 controls when the manifold pressure drops. Thismeans that the signal appearing on the terminal 282 rises in unison withmanifold pressure, but drops more slowly dependent upon the timeconstant of the integrating circuit comprising the capacitor C8 and thevariable resistor A11. The resistor A11 is adjusted to provide asuitable time constant.

The difference between the 6-volt supply and the signal on the terminal282 appears across the potentiometer A12 in series with the resistorR30. A portion of this difference is picked off at the tap of thepotentiometer A12 and applied to the + terminal of an amplifier N7-1, 2,3. The - terminal is connected to the 6-volt power supply through aresistor R32. A transistor Q6 operates to draw current through theresistor R32 so as to maintain the potential at the - terminal equal tothat picked off the tap on the potentiometer A12. The transistor Q6 iseffective until the potential at the tap reaches 6 volts at which timethe transistor Q6 is turned off, as the potential on the negativeterminal N7-2 is as high as it can get, namely with no current flowingthrough the resistor R32. In the circuit as illustrated, this occurs ata manifold pressure signal MPV of 6 volts. The sensor 94 is calibratedso that 6 volts represents atmospheric pressure of 30 inches of mercury.This establishes the point at 30 inches of mercury and 0° manifoldpressure advance MPA as shown in FIG. 14A.

As manifold pressure goes down from atmospheric, a voltage is developedacross the tapped portion of the potentiometer A12 and current flowsthrough the resistor R32 and the transistor Q6 in proportion to thesignal difference, with a characteristic slope determined by the settingof the potentiometer A12. The potentiometer A12 thus determines theslope S1 of the curve shown in FIG. 14A. The current is applied througha diode D7 and a switch S2-1 to a conductor 284 connected to the summingpoint 266. In general, it is desirable that the slope of thecharacteristic at higher pressures be greater than the slope at lowerpressures. Indeed at lower pressures the slope may be as low as zero. Toprovide a second slope, a manifold pressure break reference signal isdeveloped on a potentiometer A9. This reference signal is appliedthrough an amplifier N6-5, 6, 7 and a diode D2 to keep a referenceterminal 286 from rising above the manifold pressure break referencepotential. This means that when the manifold pressure signal at theconductor 280 rises above the reference potential on the terminal 286,the signal picked off the tap of the potentiometer A10 responds to themanifold pressure signal to a lesser degree providing a different slopeto the characteristic curve. As shown in FIG. 14A, the break in thecurve occurs at the potential corresponding to the manifold pressurebreak reference signal developed at the potentiometer A9, and the slopeS2 at lower pressures is determined by the setting of the potentiometerA10.

An idle signal IDLE is developed in an idle timing limit circuit 324when the engine is idling. The IDLE signal is applied on a conductor288, and operates at idle to turn on a transistor Q5 to apply the 6-voltpower supply potential to the inputs of the amplifiers N6-1, 2, 3 andN7-5, 6, 7, this simulating a manifold pressure signal indicating 30inches of mercury. The effect of this is that at idle there is zeromanifold pressure advance and the capacitor C8 is entirely discharged.When the engine is speeded up above idle, the manifold pressure advancesignal begins from zero and rises slowly in accordance with the timeconstant of the integrating circuit C8, A11 and instantly returns to 0°upon idling. The effect of the integrating circuit C8, A11 is that themanifold pressure advance signal can rise only slowly but can beretarded promptly. The effect of the idle signal in conjunction with theintegrating circuit C8, A11 is that the timing is retarded to providebetter emissions control during city driving when there are many stops,but slowly rises to an appropriate timing advance for better mileage inhighway driving.

With some engines under some conditions, it may be necessary ordesirable to have a relatively low timing advance to meet emissionsstandards. On the other hand, when maximum power is needed, it would bedesirable to advance the spark. Such advance is provided by a throttleposition advance circuit 292. The throttle position advance circuitreceives its input over the conductor 86 in the form of the throttleposition signal TPV. This signal is applied through a follower circuitN3-5, 6, 7 and a resistor R12 to a terminal 294. This signal is theredeveloped across a potentiometer A4 in series with a resistor R16. Aportion of the signal is picked off the tap of the potentiometer A4 andapplied to an amplifier N7-5, 6, 7, the output of which includes acurrent mirror circuit 296 which produces an output current through aresistor R23 and thence through a switch S1-4 to a conductor 298. Theamplifier N7-5, 6, 7 is biased by a voltage divider comprising aresistor R44 and a resistor R21 and by a voltage divider comprising aresistor R17 and a resistor R16. These potentials determine the throttleposition or throttle position signal TPV at which the output of theamplifier N7-5, 6, 7 drives a transistor Q5 of the current mirror 296into conduction. Above that throttle position, that is, with thethrottle wider open, the throttle position advance signal rises withthrottle position in accordance with the characteristic illustrated inFIG. 14B as the curve TPA, the throttle position advance characteristic.The curve begins at zero advance at the throttle position determined bythe bias potentials determined by the resistors R17, R16, R44 and R21.The characteristic then rises linearly in accordance with the gaindetermined by the potentiometer A4.

Engines operate at a higher temperature when running at a higher speed.Thus, when the throttle is opened to accelerate the engine, the engineis cooler than it will be when it reaches the desired speed. Thisindicates the desirability of advancing the timing upon acceleration. AΔ throttle position advance circuit 300 provides such additional sparkadvance. In this circuit, the signal at the terminal 294 is applied to adifferentiating circuit comprising a capacitor C3 and a potentiometerA3. A signal is developed at the tap of the potentiometer A3 that decayswith a time constant of perhaps one second to develop a differentialsignal. This signal is applied through an amplifier N7-1, 2, 3 and acurrent mirror circuit 302, producing an output signal ΔTPA through aswitch S1-3 to a conductor 304 connected to the summing point 274. Themagnitude of this signal is determined by the change in the throttleposition signal TPV and the setting of the potentiometer A3. Anamplifier N6-1, 2, 3 and a diode D2 operate to keep the change signalfrom going negative. That is, the signal ΔTPA can go only positive. Thismeans that additional spark advance is provided upon movement of thethrottle in the opening direction, but subtracts nothing when thethrottle is moved toward its closed position.

Because hotter ambient air results in faster burning in the cylinders,less advance is needed when the air temperature is high. To this end, atemperature limit circuit 306 is utilized to limit the advance providedby the throttle position advance circuit 292 and the Δ throttle positionadvance circuit 300. The input signals to the temperature limit circuit306 are the air density signal ADV applied on the conductor 128 and thebarometric pressure signal BPV applied on the conductor 116. Thebarometric pressure signal is applied to an amplifier N4-5, 6, 7 toproduce a corresponding signal at N4-7. This signal is applied across apotentiometer A2 in series with a resistor R5. The tap on thepotentiometer A2 thus provides a signal proportional to the barometricpressure signal BPV. Similarly, the air density signal ADV is applied toan amplifier N4-1, 2, 3 which produces at N4-1 a signal corresponding toair density. As air density is proportional to barometric pressure andinversely proportional to temperature, the signal developed at the tapof the potentiometer A2 corresponds to air density at some temperature.The setting of this tap determines a temperature TPT at which the signalat the tap is equal to the air density signal at N4-1. In the exampleillustrated by FIG. 14B, this temperature is about 170° F. The signal atthe tap of the potentiometer A2 is applied through a follower circuitN5-5, 6, 7 and applied through a resistor R6 to the - terminal of anamplifier N5-1, 2, 3. A potentiometer A1 is connected between N5-6 andN4-1. The tap on the potentiometer A1 is connected to the + terminal ofthe amplifier N5-1, 2, 3. The amplifier N5-1, 2, 3 thus amplifies aportion of the difference between the air density signal ADV and thereference signal corresponding to air density at a particular voltage asdeveloped by the potentiometer A2. The output of the amplifier N5-1, 2,3 is applied through a current mirror 308 to develop a correspondingsignal across a resistor R9. That signal is applied through an amplifierN6-5, 6, 7 and a diode D1 to the terminal 294. The setting of thepotentiometer A1 determines the slope TPT SLOPE of the characteristictemperature limit curve TPTL as shown in FIG. 14B. The effect of thetemperature limit circuit 306 is to prevent the signal at the terminal294 from rising above the signal developed by the temperature limitcircuit 306 across the resistor R9. This limits both the temperatureposition advance signal TPA and the Δ temperature position advancesignal ΔTPA, preventing either from rising above the limit TPTL set bythe temperature limit circuit 306.

Burning rate varies with the richness of the air/fuel mixture. It hasbeen determined, for example, that at least in certain engines undercertain conditions the engine begins knocking at an air/fuel ratio ofabout 16. At leaner ratios more advance can be used due to slower flamepropagation. This is achieved by a ratio control advance circuit 310 toprovide a characteristic curve RCA as shown in FIG. 14C. The ratiocontrol advance circuit receives as an input signal the ratio controlsignal RCV on the conductor 160. A reference potential is developed by avoltage divider formed by resistors R23 and R24. An amplifier N4-12, 13,14 develops this same reference potential at N8-14. The ratio controlsignal RCV is applied to an amplifier N8-1, 2, 3 to produce a signal atN8-2 that is at least as high as the ratio control signal RCV. A diodeD1 causes the signal at N8-2 to be held at the reference level developedat N8-14 should the signal RCV be below the reference potential. Apotentiometer A8 is connected between N8-2 and N8-14. The tap of thepotentiometer A8 is thus some portion of the amount that the signal atN8-2 is above the reference potential at N8-14. If the ratio controlsignal RCV is not above the reference potential, then the tap of thepotentiometer A8 remains at the reference potential. Amplifiers N8-5, 6,7 and N8-8, 9, 10 cause current to flow through a resistor R25 inproportion to this difference. This current flows through a transistorQ4 and a switch S2-2 to supply current through a conductor 312corresponding to the desired ratio control advance RCA according to thecharacteristic illustrated in FIG. 14C. The point on the curve at 0°advance is established by the voltage dividers R23 and R24. The slopeRCVG of the curve is determined by the setting of the potentiometer A8.Thus, the reference potential may be equivalent to a 16:1 air/fuelratio, so that above this ratio, the timing is advanced in accordancewith the characteristic illustrated. This current is applied to thesumming point 266 through the switch S2-2.

For the sake of emission control, engines are ordinarily operated atless than maximum efficiency. For example, they are usually run slightlyretarded during normal engine operation. There are, however, occasionswhen it is more important to assure smooth operation. Perhaps the mostdifficult time an engine has is at starting. To assure appropriateoperation while the engine is being started and until it is warmed up,it is desirable to operate at greater efficiency, even though this mayfor a time increase emissions. To this end, a start advance circuit 314provides an additional advance signal. The start advance circuitreceives its input from the ignition switch as the 12V ST signal overthe conductor 102. The 12V ST signal turns on a transistor Q12 to chargea capacitor C6 from the 6-volt power supply when the starter switch isclosed to operate the starter motor. This charge then leaks off slowlythrough a potentiometer A6 and a resistor R39 connected in series acrossthe capacitor C6. A portion of the potential across the capacitor C6 ispicked off by the tap of the potentiometer A6. As one end of thepotentiometer A6 is connected to the 6-volt power supply, the signal atthe tap of the potentiometer A6 thus is driven somewhat negative withrespect to the 6-volt power supply and gradually rises to 6 volts as thecapacitor C6 discharges through the resistor R9 and the potentiometerA6. The time constant may be set, for example, at 90 seconds. The signalon the tap of the potentiometer A6 is applied to an amplifier N3-1, 2, 3which controls the current flow through a transistor Q11 and a resistorR38 to maintain the current through the resistor R38 proportional to thedifference between 6 volts and the potential at the tap of thepotentiometer A6. This thus introduces current through a switch S1-2 andthence through a conductor 316 to the summing point 274 as the startadvance signal STA. The initial magnitude of the current is determinedby the setting of the potentiometer A6 and the duration of the startadvance signal is determined by the time constant of the circuit C6, A6,R39. 90 seconds is a convenient time for expecting the engine to bestarted and in reasonable running condition. A start advance of about10° has been found acceptable in certain engines.

When the engine is cold, the burning of the fuel in the cylinders isslower than when the engine is warmed up. To provide appropriate timingwhen the engine is cold, a cold advance signal is introduced by a coldadvance circuit 318. The input to this circuit is the cold signal CLDapplied over the conductor 158. This signal, which is high when theengine temperature is below the predetermined level, is used to turn ona transistor Q7. This provides an inverted cold signal CLD-2 on aconductor 320. At the same time, the closing of the transistor Q7 causescurrent to flow through a voltage divider formed of resistors R27 andR28, turning on a transistor Q8 and causing current to flow through aresistor R30 and a switch S1-5 and thence through a conductor 322 to thesumming point 274. The cold advance signal CLDA is the current thusdetermined by the relative magnitudes of the resistances R27, R28 andR30. A diode D3 compensates for the base to emitter drop of thetransistor Q8.

The inverted cold signal CLD-2 is also applied by way of the conductor320 to the manifold pressure advance circuit 278, where the invertedcold signal CLD-2 is applied to a diode D6. It acts to ground the outputof the manifold pressure advance circuit when the engine is cold. Thisturns off the manifold pressure advance. The purpose of this is to causethe engine to heat up faster under light load and thus to arrive morepromptly at its operating temperature where it may be caused to runleaner.

Engines often have difficulty running uniformly under idle conditions.Under normal idle conditions, the burning is incomplete in the cylindersand is completed in the hotter exhaust manifold. It is desirable toprovide stable idle ignition. This may be achieved by retarding thespark during idle from where it would otherwise be caused to occur withthe spark advance circuits described above. The idle timing limitcircuit 324 provides means for assuring a particular spark advanceduring idle conditions. The idle timing limit circuit 324 responds tothe mass flow signal MFV on the conductor 146. This signal is applied tothe + terminal of a comparator N4-1, 2, 3. A reference potential isdeveloped on a potentiometer A7 and applied to the negative terminal ofthe amplifier. Until the mass flow signal exceeds the referencepotential as set by the potentiometer A7, the potential at the amplifieroutput terminal N4-1 remains low. A potentiometer A5 and a resistor 11are connected between the terminal N4-1 and the 6-volt power supply. Thetap of the potentiometer A5 can thus be set to provide a potential inbetween. The potential on the tap A5 is applied through a followercircuit N4-5, 6, 7 and thence through a switch S2-4 through a conductor326 connected to the summing point 266. The characteristic curve IL forthe idle timing limit circuit appears in FIG. 14D. Below idle speedtiming signal break level ITB as determined by the potentiometer A7, theidle timing advance is maintained constant at its lower idle timinglimit IT as determined by the setting of the potentiometer A5. Forexample, as shown in FIG. 14D, the idle timing advance is set at 10° upto a flow rate providing an air flow signal of 0.18 volts. When the massflow signal MFV rises above that corresponding to idle air flow, thedifference between the mass flow signal MFV and the idle timingreference signal at the tap of the potentiometer A7 is amplified by theamplifier N4-1, 2, 3 causing the limit signal developed at the tap ofthe potentiometer A5 to rise in accordance with the characteristicillustrated in FIG. 14D with a slope determined by the magnitude of theresistance of a variable resistor A6. This slope should be relativelysteep to assure prompt release of the low idle timing limit when theengine is above idle. On the other hand, the slope must not be so steepso as to occasion a sharp jump in timing when the engine is operatingnear idle, as otherwise there would be sharp surges in power.

The idle timing limit signal IL operating through the output circuitN4-5, 6, 7 holds the spark advance signal as developed across theresistor R8 to the maximum permitted by the idle timing limit circuit.That is, the output of the output circuit N4-5, 6, 7 can never riseabove the idle limit potential IL developed at the tap of thepotentiometer A5.

At the same time, the signal at the terminal N4-1 is applied to the +terminal of an amplifier N5-5, 6, 7 which operates to provide a signalIDLE at the output terminal N5-7 indicative of an idle condition. TheIDLE signal is applied to control a transistor Q7 to apply the 6-voltsupply voltage to the conductor 284 through a resistor R35 when theengine is idling. This forces the output of the manifold pressureadvance circuit high when the engine is idling, assuring that the signalMPA as applied to the summing point 266 forces the signal developedacross the summing resistor R8 to the upper limit permitted, which atidle is the low idle timing limit IT.

When the engine overheats, as may be indicated by a signal on aconductor 327 when the overheat warning light goes on, it is desirableto cause the engine to idle somewhat faster to permit it to cool off.This may be achieved by disabling the idle timing limit when the engineis overheated. To this end, the signal OVERHEAT indicating overheatingmay be applied to turn on a transistor Q3 and thus lower the bias atN4-2.

The IDLE signal is also applied over the conductor 288 to the manifoldpressure advance circuit as described above to control the dumping ofthe charge on the capacitor C8, dumping the charge when the engine speeddrops below idle.

A particularly bad time for emissions is when an engine is decelerating.Under such conditions, the fuel is much reduced, as is the air intake.Some fuel will then evaporate from the intake manifold, where it mayhave accumulated along the manifold walls, and pass into the engine. Ingeneral, combustion is poor under these conditons, likely resulting inexcessive unburned hydrocarbon emissions. Of course, under theseconditions power is not needed or even desired. Hence, it is possible toreduce hydrocarbon emissions without sacrificing any desired or neededpower when the engine is decelerating. This may be achieved by assuringthat the spark is not far advanced under deceleration conditions. Thisis the function of a decel limit circuit 328 which provides adeceleration timing limit signal DECEL L in accordance with thecharacteristic illustrated in FIG. 14D. In this case, the controllinginput is the modified manifold pressure signal MPVB as applied to theconductor 280 in the manifold pressure advance circuit 278. A decelreference potential signal DPV is developed on the conductor 226 by apotentiometer A1 and an amplifier N1-5, 6, 7. This reference level DPVis set by the setting of the potentiometer A1 connected to the 6-voltpower supply. The reference DPV corresponds to a manifold pressure belowwhich the engine may be considered to be decelerating. A potentiometerA2 is connected between the conductors 226 and 280. The differencebetween the reference potential on the conductor 226 and the modifiedmanifold pressure signal MPVB therefore appears across the potentiometerA2 and a portion thereof is picked off at the tap of the potentiometer.The setting of this potentiometer thus determines the gain of thecircuit and hence the slope of the characteristic curve illustrated inFIG. 14D. This difference signal is amplified by an amplifier N1-1, 2, 3and is applied through a current mirror circuit 330 to cause the currentto flow through a resistor R6 proportional to the amount by which themodified manifold pressure signal MPVB exceeds the reference potentialDPV. When the manifold pressure signal is below this level, a transistorQ2 is non-conductive and no current therethrough flows through theresistor R6.

The base of the deceleration limit characteristic as illustrated in FIG.14D is provided at a terminal 332 by a voltage divider A3 and anamplifier N3-5, 6, 7. The setting of the potentiometer A3 determines thebase reference potential developed at the terminal 332. In absence ofconduction by the transistor Q2, the base reference potential is appliedto the + terminal of a comparator N2-5, 6, 7 which acts like thecomparator N4-5, 6, 7 to limit the decel timing advance signal, asdeveloped across the summing resistor R8 to a value no greater than thepotential at the + input terminal of the comparator N2-5, 6, 7. Thesetting of the potentiometer A3 thus determines the base decel advancelimit for the portion of the characteristic curve below the decelpressure limit DPV set at the conductor 226. This limit is shown as 20°in FIG. 14D. Above this limit, the characteristic rises with a slopedetermined by the setting of the potentiometer A2. The output signalDECEL L of the decel timing limit circuit 328 is applied through aswitch S2-5 and a conductor 334 to the summing point 266.

It is necessary that the range of timing advance be limited in orderthat the timing advance not vary so much as to permit firing of thewrong cylinder. That is, the distributor in the ignition system 24directs ignition current at the appropriate times to the respectivespark plugs in the respective cylinders. It is necessary that theignition pulse intended to create a spark in a respective cylinder occurat such time as the distributor is directing current to that cylinder.If the spark is too advanced it will appear as a late spark for apreceding cylinder. An upper limit to the spark advance is provided byan upper advance limit circuit 338. The upper advance limit circuitcomprises simply a potentiometer A4 and a comparator N2-1, 2, 3. Thiscircuit acts to prevent the output signal on an output terminal 340 fromrising above the reference potential set by the potentiometer A4. Thisthus limits the decel limit advance DECEL L at the value determined bythe potentiometer A4. As shown in the example of FIG. 14D, this limit is50°. When the switch S2-5 is closed, this also acts to limit the timingadvance signal, however developed, as it limits the voltage rise at thesumming point 266.

For similar reasons of limiting the range of the timing advance control,a lower limit of timing advance signal is provided by a lower advancelimit circuit 342 (FIG. 12). The lower advance limit circuit comprises apotentiometer A9 which determines the lower reference limit, anamplifier N8-1, 2, 3 and an output diode D5. The diode D5 causes a lowerlimit signal LL to be coupled through a switch S1-6 to a conductor 344which is connected to the summing point 274 whenever the lower referencelimit is greater than the timing advance signal as otherwise developedat the summing point 274. This prevents the timing advance signal fromfalling below this reference level LL. Under many circumstances, nolower limit is necessary because the various timing advance circuitsthemselves assure sufficient advance of the spark as to preclude firingin the wrong cylinder.

A capacitor C4 is connected across the summing resistor R8 and acts tosmooth out rapid changes in the timing advance. Thus, the various timingadvance circuits provide current to the summing resistor R8 and developa cumulative signal which is limited by the various limit circuits andis then applied through the amplifier N3-1, 2, 3 as the timing controlsignal TCV applied over the conductor 236 to the ignition timingcontroller 11.

Referring to FIG. 14, a switch position chart shown in FIG. 14Eindicates which of the various switches are operated to put the variouslimit circuits or timing advance circuits into the timing advancesystem. Normally, all of the various control circuits are in the system.However, there are many engines for which the throttle position advancecircuit and the Δ throttle position advance circuit are not needed. Theswitch position indicated as PROG represents a programming position andrefers to a switch S2-3 which is part of a test circuit 356 connected bya conductor 358 to the summing point 266. The test circuit 356 applies afull test signal to the summing point 266 and forces the timing to itslimit as an aid to checking the setting of the circuits.

Although a preferred embodiment of the circuitry of the controller 2 hasbeen shown, various modifications may be made therein within the scopeof the present invention. For example, as mentioned above, not all ofthe timing circuits need be switched into the timing control system atthe same time. Different engines and the different automobiles in whichthe engines are to be used may dictate other operating controls withinthe spirit of the present invention. Further, the various limits,reference potentials, and slopes of various characteristics can beadjusted within the skill of the art to meet particular operatingrequirements and to meet various legal requirements for mileage andemissions control.

In the exemplary circuits, typical components and component values arespecified on the drawings. It is to be understood that various DC powersupplies are furnished in a conventional manner and that the variousintegrated circuits are supplied with power in the usual manner.

What is claimed is:
 1. In an electronic controller for an internalcombustion engine having a throttle for controlling the flow of air intoan intake manifold wherein rate of air flow into the engine is measuredby producing an air flow signal systematically related to the rate ofair flow, and rate of fuel flow into the engine is measured by producinga fuel flow signal systematically related to the rate of fuel flow, saidelectronic controller including means for producing a ratio controlsignal corresponding to a respective air/fuel ratio, and meansresponsive to said air flow signal, said fuel flow signal and said ratiocontrol signal for controlling fuel flow as to make the ratio of airflow to fuel flow substantially equal to said respective air/fuel ratio,the improvement wherein said means for producing said ratio controlsignal comprises means for providing a base run ratio signalcorresponding to a respective run air/fuel ratio suitable for steadystate engine operation, means for providing a temperature referencesignal corresponding to a reference engine temperature, means responsiveto engine temperature and said temperature reference signal formodifying said run ratio signal in systematic relation to enginetemperature when said engine temperature is below said reference enginetemperature to produce a run ratio signal corresponding to an air/fuelratio systematically decreasing with decrease in engine temperaturebelow said reference engine temperature, means for providing at leastone other ratio signal corresponding to a respective air/fuel ratiosuitable for engine operation under certain other conditions,discriminating output means responsive to applied ratio signals forproducing a ratio control signal corresponding to the lowest air/fuelratio of any applied ratio signal, and means for applying said run ratiosignal and said at least one other ratio signal to said output means. 2.In an electronic controller for an internal combustion engine having athrottle for controlling the flow of air into an intake manifold whereinrate of air flow into the engine is measured by producing an air flowsignal systematically related to the rate of air flow, and rate of fuelinto the engine is measured by producing a fuel flow signalsystematically related to the rate of fuel flow, said electroniccontroller including means for producing a ratio control signalcorresponding to a respective air/fuel ratio, and means responsive tosaid air flow signal, said fuel flow signal and said ratio controlsignal for controlling fuel flow as to make the ratio of air flow tofuel flow substantially equal to said respective air/fuel ratio, theimprovement wherein said means for producing said ratio control signalcomprises means for providing a run ratio signal corresponding to arespective run air/fuel ratio suitable for engine operation undercertain conditions, means for providing at least one other ratio signalcorresponding to a respective air/fuel ratio suitable for engineoperation under certain other conditions, discriminating output meansresponsive to applied ratio signals for producing a ratio control signalcorresponding to the lowest air/fuel ratio of any applied ratio signal,and means for applying said run ratio signal and said at least one otherratio signal to said output means.
 3. In an electronic controller for aninternal combustion engine having a throttle for controlling the flow ofair into an intake manifold wherein rate of air flow into the engine ismeasured by producing an air flow signal systematically related to therate of air flow, and rate of fuel flow into the engine is measured byproducing a fuel flow signal systematically related to the rate of fuelflow, said electronic controller including means for producing a ratiocontrol signal corresponding to a respective air/fuel ratio, and meansresponsive to said air flow signal, said fuel flow signal and said ratiocontrol signal for controlling fuel flow as to make the ratio of airflow to fuel flow substantially equal to said respective air/fuel ratio,the improvement wherein said means for producing said ratio controlsignal comprises means for providing a manifold pressure referencesignal corresponding to a reference pressure in said manifold, means forproviding a base decel ratio signal corresponding to a respective decelair/fuel ratio suitable for engine operation below said referencepressure, means responsive to pressure in said manifold and saidmanifold pressure reference signal for modifying said base decel ratiosignal in systematic relation to manifold pressure when the manifoldpressure is above said reference pressure to produce a decel ratiosignal corresponding to an air-fuel ratio systematically increasing withincrease in manifold pressure above said reference pressure, and meansfor utilizing said decel ratio signal to produce a ratio control signal.4. In an electronic controller for an internal combustion engine havinga throttle for controlling the flow of air into an intake manifoldwherein rate of air flow into the engine is measured by producing an airflow signal systematically related to the rate of air flow, and rate offuel flow into the engine is measured by producing a fuel flow signalsystematically related to the rate of fuel flow, said electroniccontroller including means for producing a ratio control signalcorresponding to a respective air/fuel ratio, and means responsive tosaid air flow signal, said fuel flow signal and said ratio controlsignal for controlling fuel flow as to make the ratio of air flow tofuel flow substantially equal to said respective air/fuel ratio, theimprovement wherein said means for producing said ratio control signalcomprises means for providing a base run ratio signal corresponding to arespective run air/fuel ratio suitable for steady state engineoperation, means for providing a temperature reference signalcorresponding to a reference engine temperature, means responsive toengine temperature and said temperature reference signal for modifyingsaid run ratio signal in systematic relation to engine temperature whensaid engine temperature is below said reference engine temperature toproduce a run ratio signal corresponding to an air/fuel ratiosystematically decreasing with decrease in engine temperature below saidreference engine temperature, means for providing a base first powerratio signal corresponding to a respective first power air/fuel ratio,means for providing a manifold vacuum reference signal corresponding toa reference manifold vacuum, means responsive to engine manifold vacuumand said manifold vacuum reference signal for modifying said base firstpower ratio signal in systematic relation to manifold vacuum when saidmanifold vacuum is above said reference manifold vacuum to produce afirst power ratio signal corresponding to an air/fuel ratiosystematically increasing with increase in manifold vacuum, meansresponsive to engine temperature and said temperature reference signalfor further modifying said first power ratio signal in systematicrelation to engine temperature when said engine temperature is belowsaid reference engine temperature to produce a first power ratio signalcorresponding to an air/fuel ratio systematically decreasing withdecrease in engine temperature below said reference engine temperature,discriminating output means responsive to applied ratio signals forproducing a ratio control signal corresponding to the lowest air/fuelratio of any applied ratio signal, and means for applying said run ratiosignal and said first power ratio signal to said output means.
 5. In anelectronic controller for an internal combustion engine having athrottle for controlling the flow of air into an intake manifold whereinrate of air flow into the engine is measured by producing an air flowsignal systematically related to the rate of air flow, and rate of fuelflow into the engine is measured by producing a fuel flow signalsystematically related to the rate of fuel flow, said electroniccontroller including means for producing a ratio control signalcorresponding to a respective air/fuel ratio, and means responsive tosaid air flow signal, said fuel flow signal and said ratio controlsignal for controlling fuel flow as to make the ratio of air flow tofuel flow substantially equal to said respective air/fuel ratio, theimprovement wherein said means for producing said ratio control signalcomprises means for providing a base run ratio signal corresponding to arespective run air/fuel ratio suitable for steady state engineoperation, means for providing a temperature reference signalcorresponding to a reference engine temperature, means responsive toengine temperature and said temperature reference signal for modifyingsaid run ratio signal in systematic relation to engine temperature whensaid engine temperature is below said reference engine temperature toproduce a run ratio signal corresponding to an air/fuel ratiosystematically decreasing with decrease in engine temperature below saidreference engine temperature, means for providing a base first powerratio signal corresponding to a respective first power air/fuel ratio,means for providing a manifold vacuum reference signal corresponding toa reference manifold vacuum, means responsive to engine manifold vacuumand said manifold vacuum reference signal for modifying said base firstpower ratio signal in systematic relation to manifold vacuum when saidmanifold vacuum is above said reference manifold vacuum to produce afirst power ratio signal corresponding to an air/fuel ratiosystematically increasing with increase in manifold vacuum, meansresponsive to engine throttle position for producing a second powerratio signal corresponding to a respective second power air/fuel ratioless than said first power air/fuel ratio when the throttle issubstantially wide open and otherwise corresponding to a non-limitingair/fuel ratio, means for providing a high engine speed reference signalcorresponding to a reference high engine speed, means responsive toengine speed and said high engine speed reference for providing a basethird power ratio signal corresponding to a respective third powerair/fuel ratio less than said second power air/fuel ratio when theengine speed is greater than said reference high engine speed andsystematically increasing with decrease in engine speed below saidreference high engine speed, discriminating output means responsive toapplied ratio signals for producing a ratio control signal correspondingto the lowest air/fuel ratio of any applied ratio signal, means forapplying said run ratio signal and said first and second power ratiosignals to said output means, and means responsive to throttle positionfor applying said third power ratio signal to said output means when thethrottle is substantially wide open.
 6. In an electronic controller foran internal combustion engine having a throttle for controlling the flowof air into an intake manifold wherein rate of air flow into the engineis measured by producing an air flow signal systematically related tothe rate of air flow, and rate of fuel flow into the engine is measuredby producing a fuel flow signal systematically related to the rate offuel flow, said electronic controller including means for producing aratio control signal corresponding to a respective air/fuel ratio, andmeans responsive to said air flow signal, said fuel flow signal and saidratio control signal for controlling fuel flow as to make the ratio ofair flow to fuel flow substantially equal to said respective air/fuelratio, the improvement wherein said means for producing said ratiocontrol signal comprises means for providing a base run ratio signalcorresponding to a respective run air/fuel ratio suitable for steadystate engine operation, means for providing a temperature referencesignal corresponding to a reference engine temperature, means responsiveto engine temperature and said temperature reference signal formodifying said run ratio signal in systematic relation to enginetemperature when said engine temperature is below said reference enginetemperature to produce a run ratio signal corresponding to an air/fuelratio systematically decreasing with decrease in engine temperaturebelow said reference engine temperature, means for providing an engineidle reference signal corresponding to engine operation at idle, meansfor providing a base idle ratio signal corresponding to a respectiveidle air/fuel ratio suitable for operation of the engine at idle, meansresponsive to engine operation and said engine idle reference signal formodifying said base idle ratio signal in systematic relation to engineoperation when said engine operates above idle to produce an idle ratiosignal corresponding to an air/fuel ratio systematically increasing withincrease in engine operation above idle, means responsive to enginetemperature and said temperature reference signal for further modifyingsaid idle ratio signal in systematic relation to engine temperature whensaid engine temperature is below said reference engine temperature toproduce an idle ratio signal corresponding to an air/fuel ratiosystematically decreasing with decrease in engine temperature below saidreference engine temperature, means responsive to starting to the enginefor developing a start enrich signal that decays with time, meansresponsive to said start enrich signal for further modifying said idleratio signal to correspond to a lower air/fuel ratio upon starting, suchmodification decaying with said start enrich signal, discriminatingoutput means responsive to applied ratio signals for producing a ratiocontrol signal corresponding to the lowest air/fuel ratio of any appliedratio signal, and means for applying said run ratio signal and said idleratio signal to said output means.
 7. In an electronic controller for aninternal combustion engine having a throttle for controlling the flow ofair into an intake manifold wherein rate of air flow into the engine ismeasured by producing an air flow signal systematically related to therate of air flow, and rate of fuel flow into the engine is measured byproducing a fuel flow signal systematically related to the rate of fuelflow, said electronic controller including means for producing a ratiocontrol signal corresponding to a respective air/fuel ratio, and meansresponsive to said air flow signal, said fuel flow signal and said ratiocontrol signal for controlling fuel flow as to make the ratio of airflow to fuel flow substantially equal to said respective air/fuel ratio,the improvement wherein said means for producing said ratio controlsignal comprises means for providing a base run ratio signalcorresponding to a respective run air/fuel ratio suitable for steadystate engine operation, means for providing a temperature referencesignal corresponding to a reference engine temperature, means responsiveto engine temperature and said temperature reference signal formodifying said run ratio signal in systematic relation to enginetemperature when said engine temperature is below said reference enginetemperature to produce a run ratio signal corresponding to an air/fuelratio systematically decreasing with decrease in engine temperaturebelow said reference engine temperature, means for providing an engineidle reference signal corresponding to a reference engine speed, meansfor providing a base idle ratio signal corresponding to a respectiveidle air/fuel ratio suitable for operation of the engine at idle, meansresponsive to engine speed and said engine idle reference signal formodifying said base idle ratio signal in systematic relation to enginespeed when said engine speed exceeds said reference engine speed toproduce an idle ratio signal corresponding to an air/fuel ratiosystematically increasing with increase in engine speed above saidreference engine speed, means responsive to engine temperature and saidtemperature signal for further modifying said idle ratio signal insystematic relation to engine temperature when said engine temperatureis below said reference engine temperature to produce an idle ratiosignal corresponding to an air/fuel ratio systematically decreasing withdecrease in engine temperature below said reference engine temperature,means responsive to starting of the engine for developing a start enrichsignal that decays with time, means responsive to said start enrichsignal for further modifying said idle ratio signal to correspond to alower air/fuel ratio upon starting, such modification decaying with saidstart enrich signal, discriminating output means responsive to appliedratio signals for producing a ratio control signal corresponding to thelowest air/fuel ratio of any applied ratio signal, and means forapplying said run ratio signal and said idle ratio signal to said outputmeans.
 8. In an electronic controller for an internal combustion enginehaving a throttle for controlling the flow of air into an intakemanifold wherein rate of air flow into the engine is measured byproducing an air flow signal systematically related to the rate of flow,and rate of fuel flow into the engine is measured by producing a fuelflow signal systematically related to the rate of fuel flow, saidelectronic controller including means for producing a ratio controlsignal corresponding to a respective air/fuel ratio, and meansresponsive to said air flow signal, said fuel flow signal and said ratiocontrol signal for controlling fuel flow as to make the ratio of airflow to fuel flow substantially equal to said respective air/fuel ratio,the improvement wherein said means for producing said ratio controlsignal comprises means for providing a base run ratio signalcorresponding to a respective run air/fuel ratio suitable for steadystate engine operation, means for providing a temperature referencesignal corresponding to a reference engine temperature, means responsiveto engine temperature and said temperature reference signal formodifying said run ratio signal in systematic relation to enginetemperature when said engine temperature is below said reference enginetemperature to produce a run ratio signal corresponding to an air/fuelratio systematically decreasing with decrease in engine temperaturebelow said reference engine temperature, means for providing an engineidle reference signal corresponding to a reference air flow, means forproviding a base idle ratio signal corresponding to a respective idleair/fuel ratio suitable for operation of the engine at idle, meansresponsive to rate of air flow into the engine and said engine idlereference signal for modifying said base idle ratio signal in systematicrelation to rate of air flow when said rate of air flow exceeds saidreference air flow to produce an idle ratio signal corresponding to anair/fuel ratio systematically increasing with increase in air flow abovesaid reference air flow, means responsive to engine temperature and saidtemperature reference signal for further modifying said idle ratiosignal in systematic relation to engine temperature when said enginetemperature is below said reference engine temperature to produce anidle ratio signal corresponding to an air/fuel ratio systematicallydecreasing with decrease in engine temperature below said referencesignal temperature, means responsive to starting of the engine fordeveloping a start enrich signal that decays with time, means responsiveto said start enrich signal for further modifying said idle ratio signalto correspond to a lower air/fuel ratio upon starting, such modificationdecaying with said start enrich signal, discriminating output meansresponsive to applied ratio signals for producing a ratio control signalcorresponding to the lowest air/fuel ratio of any applied ratio signal,and means for applying said run ratio signal and said idle ratio signalto said output means.
 9. In an electronic controller for an internalcombustion engine having a throttle for controlling the flow of air intoan intake manifold wherein rate of air flow into the engine is measuredby producing an air flow signal systematically related to the rate ofair flow, and rate of fuel flow into the engine is measured by producinga fuel flow signal systematically related to the rate of fuel flow, saidelectronic controller including means for producing a ratio controlsignal corresponding to a respective air/fuel ratio, and meansresponsive to said air flow signal, said fuel flow signal and said ratiocontrol signal for controlling fuel flow as to make the ratio of airflow to fuel flow substantially equal to said respective air/fuel ratio,the improvement wherein said means for producing said ratio controlsignal comprises means for providing a base run ratio signalcorresponding to a respective run air/fuel ratio suitable for steadystate engine operation, means for providing a temperature referencesignal corresponding to a reference engine temperature, means responsiveto engine temperature and said temperature reference signal formodifying said run ratio signal in systematic relation to enginetemperature when said engine temperature is below said reference enginetemperature to produce a run ratio signal corresponding to an air/fuelratio systematically decreasing with decrease in engine temperaturebelow said reference engine temperature, means for providing an engineidle reference signal corresponding to engine operation at idle, meansfor providing a base idle ratio signal corresponding to a respectiveidle air/fuel ratio suitable for operation of the engine at idle, meansresponsive to engine operation and said engine idle reference signal formodifying said base idle ratio signal in systematic relation to engineoperation when said engine operates above idle to produce an idle ratiosignal corresponding to an air/fuel ratio systematically increasing withincrease in engine operation above idle, means responsive to enginetemperature and said temperature reference signal for further modifyingsaid idle ratio signal in systematic relation to engine temperature whensaid engine temperature is below said reference engine temperature toproduce an idle ratio signal corresponding to an air/fuel ratiosystematically decreasing with decrease in engine temperature below saidreference engine temperature, means for providing a base first powerratio signal corresponding to a respective first power air/fuel ratio,means for providing a manifold vacuum reference signal corresponding toa reference manifold vacuum, means responsive to engine manifold vacuumand said manifold vacuum reference signal for modifying said base firstpower ratio signal in systematic relation to manifold vacuum when saidmanifold vacuum is above said reference manifold vacuum to produce afirst power ratio signal corresponding to an air/fuel ratiosystematically increasing with increase in manifold vacuum, meansresponsive to engine temperature and said temperature reference signalfor further modifying said first power ratio signal in systematicrelation to engine temperature when said engine temperature is belowsaid reference signal temperature to produce a first power ratio signalcorresponding to an air/fuel ratio systematically decreasing withdecrease in engine temperature below said reference engine temperature,discriminating output means responsive to applied ratio signals forproducing a ratio control signal corresponding to the lowest air/fuelratio of any applied ratio signal, and means for applying said run ratiosignal, said idle ratio signal and said first power ratio signal to saidoutput means.
 10. Apparatus according to claim 8 wherein engine idle issensed by sensing rate of air flow.
 11. In an electronic controller foran internal combustion engine having a throttle for controlling the flowof air into an intake manifold wherein rate of air flow into the engineis measured by producing an air flow signal systematically related tothe rate of air flow, and rate of fuel flow into the engine is measuredby producing a fuel flow signal systematically related to the rate offuel flow, said electronic controller including means for producing aratio control signal corresponding to a respective air/fuel ratio, andmeans responsive to said air flow signal, said fuel flow signal and saidratio control signal for controlling fuel flow as to make the ratio ofair flow to fuel flow substantially equal to said respective air/fuelratio, the improvement wherein said means for producing said ratiocontrol signal comprises means for providing a base run ratio signalcorresponding to a respective run air/fuel ratio suitable for steadystate engine operation, means for providing a temperature referencesignal corresponding to a reference engine temperature, means responsiveto engine temperature and said temperature reference signal formodifying said run ratio signal in systematic relation to enginetemperature when said engine temperature is below said reference enginetemperature to produce a run ratio signal corresponding to an air/fuelratio systematically decreasing with decrease in engine temperaturebelow said reference engine temperature, means for providing an engineidle reference signal corresponding to a reference engine speed, meansfor providing a base idle ratio signal corresponding to a respectiveidle air/fuel ratio suitable for operation of the engine at idle, meansresponsive to engine speed and said engine idle reference signal formodifying said base idle ratio signal in systematic relation to enginespeed when said engine speed exceeds said reference engine speed toproduce an idle ratio signal corresponding to an air/fuel ratiosystematically increasing with increase in engine speed above saidreference engine speed, means responsive to engine temperature and saidtemperature reference signal for further modifying said idle ratiosignal in systematic relation to engine temperature when said enginetemperature is below said reference engine temperature to produce anidle ratio signal corresponding to an air/fuel ratio systematicallydecreasing with decrease in engine temperature below said referenceengine temperature, means for providing a base first power ratio signalcorresponding to a respective first power air/fuel ratio, means forproviding a manifold vacuum reference signal corresponding to areference manifold vacuum, means responsive to engine manifold vacuumand said manifold vacuum reference signal for modifying said base firstpower ratio signal in systematic relation to manifold vacuum when saidmanifold vacuum is above said reference manifold vacuum to produce afirst power ratio signal corresponding to an air/fuel ratiosystematically increasing with increase in manifold vacuum, meansresponsive to engine temperature and said temperature reference signalfor further modifying said first power ratio signal in systematicrelation to engine temperature when said engine temperature is belowsaid reference engine temperature to produce a first power ratio signalcorresponding to an air/fuel systematically decreasing with decrease inengine temperature below said reference engine temperature,discriminating output means responsive to applied ratio signals forproducing a ratio control signal corresponding to the lowest air/fuelratio of any applied ratio signal, and means for applying said run ratiosignal, said idle ratio signal and said first power ratio signal to saidoutput means.
 12. In an electronic controller for an internal combustionengine having a throttle for controlling the flow of air into an intakemanifold wherein rate of air flow into the engine is measured byproducing an air flow signal systematically related to the rate of airflow, and rate of fuel flow into the engine is measured by producing afuel flow signal systematically related to the rate of fuel flow, saidelectronic controller including means for producing a ratio controlsignal corresponding to a respective air/fuel ratio, and meansresponsive to said air flow signal, said fuel flow signal and said ratiocontrol signal for controling fuel flow as to make the ratio of air flowto fuel flow substantially equal to said respective air/fuel ratio, theimprovement wherein said means for producing said ratio control signalcomprises means for providing a base run ratio signal corresponding to arespective run air/fuel ratio suitable for steady state engineoperation, means for providing a temperature reference signalcorresponding to a reference engine temperature, means responsive toengine temperature and said temperature reference signal for modifyingsaid run ratio signal in systematic relation to engine temperature whensaid engine temperature is below said reference engine temperature toproduce a run ratio signal corresponding to an air/fuel ratiosystematically decreasing with decrease in engine temperature below saidreference engine temperature, means for providing an engine idlereference signal corresponding to a reference air flow, means forproviding a base idle ratio signal corresponding to a respective idleair/fuel ratio suitable for operation of the engine at idle, meansresponsive to rate of air flow into the engine and said engine idlereference signal for modifying said base idle ratio signal in systematicrelation to rate of air flow when said rate of air flow exceeds saidreference air flow to produce an idle ratio signal corresponding to anair/fuel ratio systematically increasing with increase in air flow abovesaid reference air flow, means responsive to engine temperature and saidtemperature reference signal for futher modifying said idle ratio signalin systematic relation to engine temperature when said enginetemperature is below said reference engine temperature to produce anidle ratio signal corresponding to an air/fuel ratio systematicallydecreasing with decrease in engine temperature below said referenceengine temperature, means for providing a base first power ratio signalcorresponding to a respective first power air/fuel ratio, means forproviding a manifold vacuum reference signal corresponding to areference manifold vacuum, means responsive to engine manifold vacuumand said manifold vacuum reference signal for modifying said base firstpower ratio signal in systematic relation to manifold vacuum when saidmanifold vacuum is above said reference manifold vacuum to produce afirst power ratio signal corresponding to an air/fuel ratiosystematically increasing with increase in manifold vacuum, meansresponsive to engine temperature and said temperature reference signalfor further modifying said first power ratio signal in systematicrelation to engine temperature when said engine temperature is belowsaid reference engine temperature to produce a first power ratio signalcorresponding to an air/fuel ratio systematically decreasing withdecrease in engine temperature below said reference engine temperature,discriminating output means responsive to applied ratio signals forproducing a ratio control signal corresponding to the lowest air/fuelratio of any applied ratio signal, and means for applying said run ratiosignal, said idle ratio signal and said first power ratio signal to saidoutput means.
 13. In an electronic controller for an internal combustionengine having a throttle for controlling the flow of air into an intakemanifold wherein rate of air flow into the engine is measured byproducing an air flow signal systematically related to the rate of airflow, and rate of fuel flow into the engine is measured by producing afuel flow signal systematically related to the rate of fuel flow, saidelectronic controller including means for producing a ratio controlsignal corresponding to a respective air/fuel ratio, and meansresponsive to said air flow signal, said fuel flow signal and said ratiocontrol signal for controlling fuel flow as to make the ratio of airflow to fuel flow substantially equal to said respective air/fuel ratio,the improvement wherein said means for producing said ratio controlsignal comprises means for providing a base run ratio signalcorresponding to a respective run air/fuel ratio suitable for steadystate engine operation, means for providing a temperature referencesignal corresponding to a reference engine temperature, means responsiveto engine temperature and said temperature reference signal formodifying said run ratio signal in systematic relation to enginetemperature when said engine temperature is below said reference enginetemperature to produce a run ratio signal corresponding to an air/fuelratio systematically decreasing with decrease in engine temperaturebelow said reference engine temperature, means for providing an engineidle reference signal corresponding to engine operation at idle, meansfor providing a base idle ratio signal corresponding to a respectiveidle air/fuel ratio suitable for operation of the engine at idle, meansresponsive to engine operation and said engine idle reference signal formodifying said base idle ratio signal in systematic relation to engineoperation when said engine operates above idle to produce an idle ratiosignal corresponding to an air/fuel ratio systematically increasing withincrease in engine operation above idle, means responsive to enginetemperature and said temperature reference signal for further modifyingsaid idle ratio signal in systematic relation to engine temperature whensaid engine temperature is below said reference engine temperature toproduce an idle ratio signal corresponding to an air/fuel ratiosystematically decreasing with decrease in engine temperature below saidreference engine temperature, means for providing a base first powerratio signal corresponding to a respective first power air/fuel ratio,means for providing a manifold vacuum reference signal corresponding toa reference manifold vacuum, means responsive to engine manifold vacuumand said manifold vacuum reference signal for modifying said base firstpower ratio signal in systematic relation to manifold vacuum when saidmanifold vacuum is above said reference manifold vacuum to produce afirst power ratio signal corresponding to an air/fuel ratiosystematically increasing with increase in manifold vacuum, meansresponsive to engine throttle position for producing a second powerratio signal corresponding to a respective second power air/fuel ratioless than said first power air/fuel ratio when the throttle issubstantially wide open and corresponding otherwise to a non-limitingair/fuel ratio, means for providing a high engine speed reference signalcorresponding to a reference high engine speed, means responsive toengine speed and said high engine speed reference signal for providing abase third power ratio signal corresponding to a respective third powerair/fuel ratio less than said second power air/fuel ratio when theengine speed is greater than said reference high engine speed andsystematically increasing with decrease in engine speed below saidreference high engine speed, discriminating output means responsive toapplied ratio signals for producing a ratio control signal correspondingto the lowest air/fuel ratio of any applied ratio signal, means forapplying said run ratio signal, said idle ratio signal and said firstand second power ratio signals to said output means, and meansresponsive to throttle position for applying said third power ratiosignal to said output means when the throttle is substantially wideopen.
 14. In an electronic controller for an internal combustion enginehaving a throttle for controlling the flow of air into an intakemanifold wherein rate of air flow into the engine is measured byproducing an air flow signal systematically related to the rate of airflow, and rate of fuel flow into the engine is measured by producing afuel flow signal systematically related to the rate of fuel flow, saidelectronic controller including means for producing a ratio controlsignal corresponding to a respective air/fuel ratio, and meansresponsive to said air flow signal, said fuel flow signal and said ratiocontrol signal for controlling fuel flow as to make the ratio of airflow to fuel flow substantially equal to said respective air/fuel ratio,the improvement wherein said means for producing said ratio controlsignal comprises means for providing a base run ratio signalcorresponding to a respective run air/fuel ratio suitable for steadystate engine operation, means for providing a temperature referencesignal corresponding to a reference engine temperature, means responsiveto engine temperature and said temperature reference signal formodifying said run ratio signal in systematic relation to enginetemperature when said engine temperature is below said reference enginetemperature to produce a run ratio signal corresponding to an air/fuelratio systematically decreasing with decrease in engine temperaturebelow said reference engine temperature, means for providing an engineidle reference signal corresponding to a reference engine speed, meansfor providing a base idle ratio signal corresponding to a respectiveidle air/fuel ratio suitable for operation of the engine at idle, meansresponsive to engine speed and said engine idle reference signal formodifying said base idle ratio signal in systematic relation to enginespeed when said engine speed exceeds said reference engine speed toproduce an idle ratio signal corresponding to an air/fuel ratiosystematically increasing with increase in engine speed above saidreference engine speed, means responsive to engine temperature and saidtemperature reference signal for further modifying said idle ratiosignal in systematic relation to engine temperature when said enginetemperature is below said reference engine temperature to produce anidle ratio signal corresponding to an air/fuel ratio systematicallydecreasing with decrease in engine temperature below said referenceengine temperature, means for providing a base first power ratio signalcorresponding to a respective first power air/fuel ratio, means forproviding a manifold vacuum reference signal corresponding to areference manifold vacuum, means responsive to engine manifold vacuumand said manifold vacuum reference signal for modifying said base firstpower ratio signal in systematic relation to manifold vacuum when saidmanifold vacuum is above said reference manifold vacuum to produce afirst power ratio signal corresponding to an air/fuel ratiosystematically increasing with increase in manifold vacuum, meansresponsive to engine throttle position for producing a second powerratio signal corresponding to a respective second power air/fuel ratioless than said first power air/fuel ratio when the throttle issubstantially wide open and corresponding otherwise to a non-limitingair/fuel ratio, means for providing a high engine speed reference signalcorresponding to a reference high engine speed, means responsive toengine speed and said high engine speed reference signal for providing abase third power ratio signal corresponding to a respective third powerair/fuel ratio less than said second power air/fuel ratio when theengine speed is greater than said reference high engine speed andsystematically increasing with decrease in engine speed below saidreference high engine speed, discriminating output means responsive toapplied ratio signals for producing a ratio control signal correspondingto the lowest air/fuel ratio of any applied ratio signal, means forapplying said run ratio signal, said idle ratio signal and said firstand second power ratio signals to said output means, and meansresponsive to throttle position for applying said third power ratiosignal to said output means when the throttle is substantially wideopen.
 15. In an electronic controller for an internal combustion enginehaving a throttle for controlling the flow of air into an intakemanifold wherein rate of air flow into the engine is measured byproducing an air flow signal systematically related to the rate of airflow, and rate of fuel flow into the engine is measured by producing afuel flow signal systematically related to the rate of fuel flow, saidelectronic controller including means for producing a ratio controlsignal corresponding to a respective air/fuel ratio, and meansresponsive to said air flow signal, said fuel flow signal and said ratiocontrol signal for controlling fuel flow as to make the ratio of airflow to fuel flow substantially equal to said respective air/fuel ratio,the improvement wherein said means for producing said ratio controlsignal comprises means for providing a base run ratio signalcorresponding to a respective run air/fuel ratio suitable for steadystate engine operation, means for providing a temperature referencesignal corresponding to a reference engine temperature, means responsiveto engine temperature and said temperature reference signal formodifying said run ratio signal in systematic relation to enginetemperature when said engine temperature is below said reference enginetemperature to produce a run ratio signal corresponding to an air/fuelratio systematically decreasing with decrease in engine temperaturebelow said reference engine temperature, means for providing an engineidle reference signal corresponding to a reference air flow, means forproviding a base idle ratio signal corresponding to a respective idleair/fuel ratio suitable for operation of the engine at idle, meansresponsive to rate of air flow into the engine and said engine idlereference signal for modifying said base idle ratio signal in systematicrelation to rate of air flow when said rate of air flow exceeds saidreference air flow to produce an idle ratio corresponding to an air/fuelratio systematically increasing with increase in air flow above saidreference air flow, means responsive to engine temperature and saidtemperature reference signal for further modifying said idle ratiosignal in systematic relation to engine temperature when said enginetemperature is below said reference engine temperature to produce anidle ratio signal corresponding to an air/fuel ratio systematicallydecreasing with decrease in engine temperature below said referenceengine temperature, means for providing a base first power ratio signalcorresponding to a respective first power air/fuel ratio, means forproviding a manifold vacuum reference signal corresponding to areference manifold vacuum, means responsive to engine manifold vacuumand said manifold vacuum reference signal for modifying said base firstpower ratio signal in systematic relation to manifold vacuum when saidmanifold vacuum is above reference manifold vacuum to produce a firstpower ratio signal corresponding to an air/fuel ratio systematicallyincreasing with increase in manifold vacuum, means responsive to enginethrottle position for producing a second power ratio signalcorresponding to a respective second power air/fuel ratio less than saidfirst power air/fuel ratio when the throttle is substantially wide openand corresponding otherwise to a non-limiting air/fuel ratio, means forproviding a high engine speed reference signal corresponding to areference high engine speed, means responsive to engine speed and saidhigh engine speed reference signal for providing a base third powerratio signal corresponding to a respective third power air/fuel ratioless than said second power air/fuel ratio when the engine speed isgreater than said reference high engine speed and systematicallyincreasing with decrease in engine speed below said reference highengine speed, discriminating output means responsive to applied ratiosignals for producing a ratio control signal corresponding to the lowestair/fuel ratio of any applied ratio signal, means for applying said runratio signal, said idle ratio signal and said first and second powerratio signals to said output means, and means responsive to throttleposition for applying said third power ratio signal to said output meanswhen the throttle is substantially wide open.
 16. In an electroniccontroller for an internal combustion engine having a throttle forcontrolling the flow of air into an intake manifold wherein rate of airflow into the engine is measured by producing an air flow signalsystematically related to the rate of air flow, and rate of fuel flowinto the engine is measured by producing a fuel flow signalsystematically related to the rate of fuel flow, said electroniccontroller including means for producing a ratio control signalcorresponding to a respective air/fuel ratio, and means responsive tosaid air flow signal, said fuel flow signal and said ratio controlsignal for controlling fuel flow as to make the ratio of air flow tofuel flow substantially equal to said respective air/fuel ratio, theimprovement wherein said means for producing said ratio control signalcomprises means for providing a run ratio signal corresponding to arespective run air/fuel ratio suitable for engine operation undercertain conditions; means for providing at least one other ratio signalcorresponding to a respective air/fuel ratio suitable for engineoperation under certain other conditions, said means for providing atleast one other ratio signal including means for providing a base firstpower ratio signal corresponding to a respective first power air/fuelratio, means for providing a manifold vacuum reference signalcorresponding to a reference manifold vacuum, means responsive to enginemanifold vacuum and said manifold vacuum reference signal for modifyingsaid base first power ratio signal in systematic relation to manifoldvacuum when said manifold vacuum is above said reference manifold vacuumto produce a first power ratio signal corresponding to an air/fuel ratiosystematically increasing with increase in manifold vacuum, means forproviding a temperature reference signal corresponding to a referenceengine temperature, and means responsive to engine temperature and saidtemperature reference signal for further modifying said first powerratio signal in systematic relation to engine temperature when saidengine temperature is below said reference engine temperature to producea first power ratio signal corresponding to an air/fuel ratiosystematically decreasing with decrease in engine temperature below saidreference engine temperature; discriminating output means responsive toapplied ratio signals for producing a ratio control signal correspondingto the lowest air/fuel ratio of any applied ratio signal; and means forapplying said run ratio signal and said first power ratio signal to saidoutput means.
 17. In an electronic controller for an internal combustionengine having a throttle for controlling the flow of air into an intakemanifold wherein rate of air flow into the engine is measured byproducing an air flow signal systematically related to the rate of airflow, and rate of fuel flow into the engine is measured by producing afuel flow signal systematically related to the rate of fuel flow, saidelectronic controller including means for producing a ratio controlsignal corresponding to a respective air/fuel ratio, and meansresponsive to said air flow signal, said fuel flow signal and said ratiocontrol signal for controlling fuel flow as to make the ratio of airflow to fuel flow substantially equal to said respective air/fuel ratio,the improvement wherein said means for producing said ratio controlsignal comprises means for providing a run ratio signal corresponding toa respective run air/fuel ratio suitable for engine operation undercertain conditions; means for providing at least one other ratio signalcorresponding to a respective air/fuel ratio suitable for engineoperation under certain other conditions, said means for providing atleast one other ratio signal including means for providing a base firstpower ratio signal corresponding to a respective first power air/fuelratio, means for providing a manifold vacuum reference signalcorresponding to a reference manifold vacuum, means responsive to enginemanifold vaccum and said manifold vacuum reference signal for modifyingsaid base first power ratio signal in systematic relation to manifoldvacuum when said manifold vacuum is above said reference manifold vacuumto produce a first power ratio signal corresponding to an air/fuel ratiosystematically increasing with increase in manifold vacuum, meansresponsive to engine throttle position for producing a second powerratio signal corresponding to a respective second power air/fuel ratioless than said first power air/fuel ratio when the throttle issubstantially wide open and corresponding otherwise to a non-limitingair/fuel ratio, means for providing a high engine speed reference signalcorresponding to a reference high engine speed, means responsive toengine speed and said high engine speed reference signal for providing abase third power ratio signal corresponding to a respective third powerair/fuel ratio less than said second power air/fuel ratio when theengine speed is greater than said reference high engine speed andsystematically increasing with decrease in engine speed below saidreference high engine speed; discriminating output means responsive toapplied ratio signals for producing a ratio control signal correspondingto the lowest air/fuel ratio of any applied ratio signal; and means forapplying said run ratio signal and said at least one other ratio signalto said output means, wherein said means for applying said at least oneother ratio signal includes means for applying said first and secondpower ratio signals to said output means, and means responsive tothrottle position for applying said third power ratio signal to saidoutput means when the throttle is substantially wide open.
 18. In anelectronic controller for an internal combustion engine having athrottle for controlling the flow of air into an intake manifold whereinrate of air flow into the engine is measured by producing an air flowsignal systematically related to the rate of air flow, and rate of fuelflow into the engine is measured by producing a fuel flow signalsystematically related to the rate of fuel flow, said electroniccontroller including means for producing a ratio control signalcorresponding to a respective air/fuel ratio, and means responsive tosaid air flow signal, said fuel flow signal and said ratio controlsignal for controlling fuel flow as to make the ratio of air flow tofuel flow substantially equal to said respective air/fuel ratio, theimprovement wherein said means for producing said ratio control signalcomprises means for providing a run ratio signal corresponding to arespective run air/fuel ratio suitable for engine operation undercertain conditions; means for providing at least one other ratio signalcorresponding to a respective air/fuel ratio suitable for engineoperation under certain other conditions, said means for providing atleast one other ratio signal including means for providing an engineidle reference signal corresponding to engine operation at idle, meansfor providing a base idle ratio signal corresponding to a respectiveidle air/fuel ratio suitable for operation of the engine at idle, meansresponsive to engine operation and said engine idle reference signal formodifying said base idle ratio signal in systematic relation to engineoperation when said engine operates above idle to produce an idle ratiosignal corresponding to an air/fuel ratio systematically increasing withincrease in engine operation above idle, means for providing atemperature reference signal corresponding to a reference enginetemperature, and means responsive to engine temperature and saidtemperature reference signal for further modifying said idle ratiosignal in systematic relation to engine temperature when said enginetemperature is below said reference engine temperature to produce anidle ratio signal corresponding to an air/fuel ratio systematicallydecreasing with decrease in engine temperature below said referenceengine temperature; discriminating output means responsive to appliedratio signals for producing a ratio control signal corresponding to thelowest air/fuel ratio of any applied ratio signal; and means forapplying said run ratio signal and said at least one other ratio signalto said output means, said means for applying said at least one otherratio signal including means for applying said idle ratio signal to saidoutput means.
 19. In an electronic controller for an internal combustionengine having a throttle for controlling the flow of air into an intakemanifold wherein rate of air flow into the engine is measured byproducing an air flow signal systematically related to the rate of airflow, and rate of fuel flow into the engine is measured by producing afuel flow signal systematically related to the rate of fuel flow, saidelectronic controller including means for producing a ratio controlsignal corresponding to a respective air/fuel ratio, and meansresponsive to said air flow signal, said fuel flow signal and said ratiocontrol signal for controlling fuel flow as to make the ratio of airflow to fuel flow substantially equal to said respective air/fuel ratio,the improvement wherein said means for producing said ratio controlsignal comprises means for providing a run ratio signal corresponding toa respective run air/fuel ratio suitable for engine operation undercertain conditions; means for providing at least one other ratio signalcorresponding to a respective air/fuel ratio suitable for engineoperation under certain other conditions, said means for providing atleast one other ratio signal including means for providing an engineidle reference signal corresponding to a reference engine speed, meansfor providing a base idle ratio signal corresponding to a respectiveidle air/fuel ratio suitable for operation of the engine at idle, meansresponsive to engine speed and said engine idle reference signal formodifying said base idle ratio signal in systematic relation to enginespeed when said engine speed exceeds said refernce engine speed toproduce an idle ratio signal corresponding to an air/fuel ratiosystematically increasing with increase in engine speed above saidreference engine speed, means for providing a temperature referencesignal corresponding to a reference engine temperature, and meansresponsive to engine temperature and said temperature reference signalfor further modifying said idle ratio signal in systematic relation toengine temperature when said engine temperature is below said referenceengine temperature to produce an idle ratio signal corresponding to anair/fuel ratio systematically decreasing with decrease in enginetemperature below said reference engine temperature; discriminatingoutput means responsive to applied ratio signals for producing a ratiocontrol signal corresponding to the lowest air/fuel ratio of any appliedratio signal; and means for applying said run ratio signal and said atleast one other ratio signal to said output means, said means forapplying said at least one other ratio signal including means forapplying said idle ratio signal to said output means.
 20. In anelectronic controller for an internal combustion engine having athrottle for controlling the flow of air into an intake manifold whereinrate of air flow into the engine is measured by producing an air flowsignal systematically related to the rate of air flow, and rate of fuelflow into the engine is measured by producing a fuel flow signalsystematically related to the rate of fuel flow, said electroniccontroller including means for producing a ratio control signalcorresponding to a respective air/fuel ratio, and means responsive tosaid air flow signal, said fuel flow signal and said ratio controlsignal for controlling fuel flow as to make the ratio of air flow tofuel flow substantially equal to said respective air/fuel ratio, theimprovement wherein said means for producing said ratio control signalcomprises means for providing a run ratio signal corresponding to arespective run air/fuel ratio suitable for engine operation undercertain conditions; means for providing at least one other ratio signalcorresponding to a respective air/fuel ratio suitable for engineoperation under certain other conditions, said means for providing atleast one other ratio signal including means for providing an engineidle reference signal corresponding to a reference air flow, means forproviding a base idle ratio signal corresponding to a respective idleair/fuel ratio suitable for operation of the engine at idle, meansresponsive to rate of air flow into the engine and said engine idlereference signal for modifying said base idle ratio signal in systematicrelation to rate of air flow when said rate of air flow exceeds saidreference air flow to produce an idle ratio corresponding to an air/fuelratio systematically increasing with increase in air flow above saidreference air flow, means for providing a temperature reference signalcorresponding to a reference engine temperature, and means responsive toengine temperature and said temperature reference signal for furthermodifying said idle ratio signal in systematic relation to enginetemperature when said engine temperature is below said reference enginetemperature to produce an idle ratio signal corresponding to an air/fuelratio systematically decreasing with decrease in engine temperaturebelow said reference engine temperature; discriminating output meansresponsive to applied ratio signals for producing a ratio control signalcorresponding to the lowest air/fuel ratio of any applied ratio signal;and means for applying said run ratio signal and said at least one otherratio signal to said output means, said means for applying said at leastone other ratio signal including means for applying said idle ratiosignal to said output means.
 21. Apparatus according to claim 1 whereinsaid means for modifying said run ratio includes means responsive tosaid engine temperature and said temperature reference signal fordeveloping a temperature control signal systematically related to thedifference between said engine temperature and said reference enginetemperature, and means for multiplicatively combining said temperaturecontrol signal and said base run ratio signal to produce said run ratiosignal corresponding to an air/fuel ratio systematically decreasing withdecrease in engine temperature below said reference engine temperature.22. Apparatus according to claim 1 including means for providing a basefirst power ratio signal corresponding to a respective first powerair/fuel ratio, means for providing a manifold vacuum reference signalcorresponding to a reference manifold vacuum, means responsive to enginemanifold vacuum and said manifold vacuum reference signal for modifyingsaid base first power ratio signal in systematic relation to manifoldvacuum when said manifold vacuum is above said reference manifold vacuumto produce a first power ratio signal corresponding to an air/fuel ratiosystematically increasing with increase in manifold vacuum, and meansfor applying said first power ratio signal to said output means. 23.Apparatus according to claim 22 including means responsive to enginethrottle position for producing a second power ratio signalcorresponding to a respective second power air/fuel ratio less than saidfirst power air/fuel ratio when the throttle is substantially wide openand otherwise correspondng to a non-limiting air/fuel ratio, and meansfor applying said second power ratio signal to said output means. 24.Apparatus according to claim 1 including means for providing an engineidle reference signal corresponding to engine operation at idle, meansfor providing a base idle ratio signal corresponding to a respectiveidle air/fuel ratio suitable for operation of the engine at idle, meansresponsive to engine operation and said engine idle reference signal formodifying said base idle ratio signal in systematic relation to engineoperation when said engine operates above idle to produce an idle ratiosignal corresponding to an air/fuel ratio systematically increasing withincrease in engine operation above idle, and means for applying saididle ratio signal to said output means.
 25. Apparatus according to claim24 wherein engine idle is sensed by sensing rate of air flow. 26.Apparatus according to claim 24 wherein engine idle is sensed by sensingengine speed.
 27. Apparatus according to claim 1 including means forproviding an engine idle reference signal corresponding to a referenceengine speed, means for providing a base idle ratio signal correspondingto a respective idle air/fuel ratio suitable for operation of the engineat idle, means responsive to engine speed and said engine idle referencesignal for modifying said base idle ratio signal in systematic relationto engine speed when said engine speed exceeds said reference enginespeed to produce an idle ratio signal corresponding to an air/fuel ratiosystematically increasing with increase in engine speed above saidreference engine speed, and means for applying said idle ratio signal tosaid output means.
 28. Apparatus according to claim 1 including meansfor providing an engine idle reference signal corresponding to areference air flow, means for providing a base idle ratio signalcorresponding to a respective idle air/fuel ratio suitable for operationof the engine at idle, means responsive to rate of air flow into theengine and said engine idle reference signal for modifying said baseidle ratio signal in systematic relation to rate of air flow when saidrate of air flow exceeds said reference air flow to produce an idleratio signal corresponding to an air/fuel ratio systematicallyincreasing with increase in air flow above said reference air flow, andmeans for applying said idle ratio signal to said output means. 29.Apparatus according to any one of claims 24 to 28 including meansresponsive to engine temperature and said temperature reference signalfor further modifying said idle ratio signal in systematic relation toengine temperature when said engine temperature is below said referenceengine temperature to produce an idle ratio signal corresponding to anair/fuel ratio systematically decreasing with decrease in enginetemperature below said reference engine temperature.
 30. Apparatusaccording to claim 29 including means for providing a base first powerratio signal corresponding to a respective first power air/fuel ratio,means for providing a manifold vacuum reference signal corresponding toa reference manifold vacuum, means responsive to engine manifold vacuumand said manifold vacuum reference signal for modifying said base firstpower ratio signal in systematic relation to manifold vacuum when saidmanifold vacuum is above said reference manifold vacuum to produce afirst power ratio signal corresponding to an air/fuel ratiosystematically increasing with increase in manifold vacuum, and meansfor applying said first power ratio signal to said output means. 31.Apparatus according to claim 30 including means responsive to enginethrottle position for producing a second power ratio signalcorresponding to a respective second power air/fuel ratio less than saidfirst power air/fuel ratio when the throttle is substantially wide openand corresponding otherwise to a non-limiting air/fuel ratio, and meansfor applying said second power ratio signal to said output means. 32.Apparatus according to any one of claims 1, 22, 23 and 24 includingmeans for providing a manifold pressure reference signal correspondingto a reference pressure in said manifold, means for providing a basedecel ratio signal corresponding to a respective decel air/fuel ratiosuitable for engine operation below said reference pressure, meansresponsive to pressure in said manifold and said manifold pressurereference signal for modifying said base decel ratio signal insystematic relation to manifold pressure when the manifold pressure isabove said reference pressure to produce a decel ratio signalcorresponding to an air/fuel ratio systematically increasing withincrease in manifold pressure above said reference pressure, and meansfor applying said decel ratio signal to said output means.
 33. Apparatusaccording to claim 29 including means for providing a manifold pressurereference signal corresponding to a reference pressure in said manifold,means for providing a base decel ratio signal corresponding to arespective decel air/fuel ratio suitable for engine operation below saidreference pressure, means responsive to pressure in said manifold andsaid manifold pressure reference signal for modifying said base decelratio signal in systematic relation to manifold pressure when themanifold pressure is above said reference pressure to produce a decelratio signal corresponding to an air/fuel ratio systematicallyincreasing with increase in manifold pressure above said referencepressure, and means for applying said decel ratio signal to said outputmeans.
 34. Apparatus according to claim 2 wherein said means forproviding at least one other ratio signal includes means for providing abase first power ratio signal corresponding to a respective first powerair/fuel ratio, means for providing a manifold vacuum reference signalcorresponding to a reference manifold vacuum, and means responsive toengine manifold vacuum and said manifold vacuum reference signal formodifying said base first power ratio signal in systematic relation tomanifold vacuum when said manifold vacuum is above said referencemanifold vacuum to produce a first power ratio signal corresponding toan air/fuel ratio systematically increasing with increase in manifoldvacuum, and wherein said means for applying said at least one otherratio signal includes means for applying said first power ratio signalto said output means.
 35. Apparatus according to claim 34 wherein saidmeans for providing at least one other ratio signal includes meansresponsive to engine throttle position for producing a second powerratio signal corresponding to a respective second power air/fuel ratioless than said first power air/fuel ratio when the throttle issubstantially wide open and otherwise corresponding to a non-limitingair/fuel ratio, and wherein said means for applying said at least oneother ratio signal includes means for applying said second power ratiosignal to said output means.
 36. Apparatus according to claim 2 whereinsaid means for providing at least one other ratio signal includes meansfor providing an engine idle reference signal corresponding to engineoperation at idle, means for providing a base idle ratio signalcorresponding to a respective idle air/fuel ratio suitable for operationof the engine at idle, and means responsive to engine operation and saidengine idle reference signal for modifying said base idle ratio signalin systematic relation to engine operation when said engine operatesabove idle to produce an idle ratio signal corresponding to an air/fuelratio systematically increasing with increase in engine operation aboveidle, and wherein said means for applying said at least one other ratiosignal includes means for applying said idle ratio signal to said outputmeans.
 37. Apparatus according to claim 36 wherein engine idle is sensedby sensing rate of air flow.
 38. Apparatus according to claim 36 whereinengine idle is sensed by sensing engine speed.
 39. Apparatus accordingto claim 2 wherein said means for providing at least one other ratiosignal includes means for providing an engine idle reference signalcorresponding to a reference engine speed, means for providing a baseidle ratio signal corresponding to a respective idle air/fuel ratiosuitable for operation of the engine at idle, and means responsive toengine speed and said engine idle reference signal for modifying saidbase idle ratio signal in systematic relation to engine speed when saidengine speed exceeds said reference engine speed to produce an idleratio signal corresponding to an air/fuel ratio systematicallyincreasing with increase in engine speed above said reference enginespeed, and wherein said means for applying said at least one other ratiosignal includes means for applying said idle ratio signal to said outputmeans.
 40. Apparatus according to claim 2 wherein said means forproviding at least one other ratio signal includes means for providingan engine idle reference signal corresponding to a reference air flow,means for providing a base idle signal corresponding to a respectiveidle air/fuel ratio suitable for operation of the engine at idle, andmeans responsive to rate of air flow into the engine and said engineidle reference signal for modifying said base idle ratio signal insystematic relation to rate of air flow when said rate of air flowexceeds said reference air flow to produce an idle ratio signalcorresponding to an air/fuel ratio systematically increasing withincrease in air flow above said reference air flow, and wherein saidmeans for applying said at least one other ratio signal includes meansfor applying said idle ratio signal to said output means.
 41. Apparatusaccording to any one of claims 17 to 20 including means responsive tostarting of the engine for developing a start enrich signal that decayswith time, and means responsive to said start enrich signal for furthermodifying said idle ratio signal to correspond to a lower air/fuel ratioupon starting, such modification decaying with said start enrich signal.42. Apparatus according to any one of claims 17 to 20 wherein said meansfor providing at least one other ratio signal includes means forproviding a base first power ratio signal corresponding to a respectivefirst power air/fuel ratio, means for providing a manifold vacuumreference signal corresponding to a reference manifold vacuum, and meansresponsive to engine manifold vacuum and said manifold vacuum referencesignal for modifying said base first power ratio signal in systematicrelation to manifold vacuum when said manifold vacuum is above saidreference manifold vacuum to produce a first power ratio signalcorresponding to an air/fuel ratio systematically increasing wihincrease in manifold vacuum, and wherein said means for applying said atleast one other ratio signal includes means for applying said firstpower ratio signal to said output means.
 43. Apparatus according toclaim 42 including means responsive to engine temperature and saidtemperature reference signal for further modifying said first powerratio signal in systematic relation to engine temperature when saidengine temperature is below said reference engine temperature to producea first power ratio signal corresponding to an air/fuel ratiosystematically decreasing with decrease in engine temperature below saidreference engine temperature.
 44. Apparatus according to claim 42wherein said means for providing at least one other ratio signalincludes means responsive to engine throttle position for producing asecond power ratio signal corresponding to a respective second powerair/fuel ratio less than said first power air/fuel ratio when thethrottle is substantially wide open and corresponding otherwise to anon-limiting air/fuel ratio, and wherein said means for applying said atleast one other ratio signal includes means for applying said secondpower ratio signal to said output means.
 45. Apparatus according toclaim 44 wherein said means for providing at least one other ratiosignal includes means for providing a high engine speed reference signalcorresponding to a reference high engine speed, and means responsive toengine speed and said high engine speed reference signal for providing abase third power ratio signal corresponding to a respective third powerair/fuel ratio less than said second power air/fuel ratio when theengine speed is greater than said reference high engine speed andsystematically increasing with decrease in engine speed below saidreference high engine speed, and wherein said means for applying said atleast one other ratio signal includes means responsive to throttleposition for applying said third power ratio signal to said output meanswhen the throttle is substantially wide open.
 46. Apparatus according toany one of claims 34, 35 and 36 wherein said means for providing atleast one other ratio signal includes means for providing a manifoldpressure reference signal corresponding to a reference pressure in saidmanifold, means for providing a base decel ratio signal corresponding toa respective decel air/fuel ratio suitable for engine operation belowsaid reference pressure, and means responsive to pressure in saidmanifold and said manifold pressure reference signal for modifying saidbase decel ratio signal in systematic relation to manifold pressure toproduce a decel ratio signal corresponding to an air/fuel ratiosystematically increasing with increase in manifold pressure above saidreference pressure, and wherein said means for applying said at leastone other ratio signal includes means for applying said decel ratiosignal to said output means.
 47. Apparatus according to any one ofclaims 16 to 20 wherein said means for providing at least one otherratio signal includes means for providing a manifold pressure referencesignal corresponding to a reference pressure in said manifold, means forproviding a base decel ratio signal corresponding to a respective decelair/fuel ratio suitable for engine operation below said referencepressure, and means responsive to pressure in said manifold and saidmanifold pressure reference signal for modifying said base decel ratiosignal in systematic relation to manifold pressure to produce a decelratio signal corresponding to an air/fuel ratio systematicallyincreasing with increase in manifold pressure above said referencepressure, and wherein said means for applying said at least one otherratio signal includes means for applying said decel ratio signal to saidoutput means.
 48. Apparatus according to claim 6 wherein engine idle issensed by sensing rate of air flow.
 49. Apparatus according to claim 6wherein engine idle is sensed by sensing engine speed.
 50. Apparatusaccording to claim 8 wherein engine idle is sensed by sensing enginespeed.
 51. Apparatus according to claim 13 wherein engine idle is sensedby sensing rate of air flow.
 52. Apparatus according to claim 13 whereinengine idle is sensed by sensing engine speed.
 53. Apparatus accordingto any one of claims 4 to 15 including means for providing a manifoldpressure reference signal corresponding to a reference pressure in saidmanifold, means for providing a base decel ratio signal corresponding toa respective decel air/fuel ratio suitable for engine operation belowsaid reference pressure, means responsive to pressure in said manifoldand said manifold pressure reference signal for modifying said basedecel ratio signal in systematic relation to manifold pressure when themanifold pressure is above said reference pressure to produce a decelratio signal corresponding to an air/fuel ratio systematicallyincreasing with increase in manifold pressure above said referencepressure, and means for applying said decel ratio signal to said outputmeans.
 54. Apparatus according to claim 18 wherein engine idle is sensedby sensing rate of air flow.
 55. Apparatus according to claim 18 whereinengine idle is sensed by sensing engine speed.